Class 10 - Science - Ch1 - Chemical Reactions & Equations Ch1 - Chemical Reactions & EquationsMCQs, Q & A, NCERT Solutions

Q1: A chemical reaction involves ina. Only breaking of bondsb. Only formation of bondsc. Both breaking and formation of bondsd. None of these

Answer: (c) Both breaking and formation of bonds

Q2: A balanced chemical equation always obeysa. Law of conservation of massb. Law of thermal equilibriumc. Law of conservation of energyd. All of the above

Answer: (a) law of conservation of mass.

Q3: Single displacement reaction involves:a. Oxidationb. Reductionc. Redoxd. Heating

Answer: (c) redox

Q4: String of ants, bees containa. Formic acidb. Vinegarc. Succinic acidd. Common Salt (NaCl)

Answer: (a) Formic acid

Q5: Some stale food gives a bad taste and a bad smell because of:a. Corrosionb. Displacementc. Heatingd. Rancidity

Answer: (d) rancidity

Q6: A red brown gas is released on heating lead nitrate. It is an example ofa. Combination reactionb. Oxidation reactionc. Decomposition reactiond. Reduction reaction

Answer: (c) Decomposition

Q7: The sign indicatesa. release of gasb. dissolution of gasc. formation of a precipitated. lowering of temperature

Answer: (c) formation of a precipitate

Q8: Why do gold and silver do not corrode?Answer:It is because they are less reactive.

Q9: What do you mean by balanced chemical equation?

Answer: An equation that has equal number of atoms of each element on both the sides of equation is called balanced chemical equation, i.e., mass of the reactants is equal to mass of the products. e.g., 2Mg + O2 2MgO

Q10: Define rancidity.Answer: When fats and oils are oxidized, they become rancid and their smell and tastechange. This process is known as rancidity.

Q11 (CBSE 2007): Write the type of reactions in the following: i. Reaction between an acid and a baseii. Rusting of iron

Answer: i. Neutralization reaction ii. Oxidation reaction

Q12: Give an example of decomposition reaction where energy is supplied in form of light.Answer: sunlight 2AgBr(s) ------------------------> 2Ag (s) + Br2(g) (Silver Bromide)

Q13: Why does copper vessel acquire green coating in rainy season?Answer: It reacts with CO2 in the atmosphere and forms a layer of basic Copper Carbonate.

Q14: What is the name of the gas which burns with a pop sound?Answer: Hydrogen gas.

Q15: Why is Hydrogen peroxide stored in coloured bottles?Answer: It is done to prevent photolytic decomposition of hydrogen peroxide.

Q16: Name the oxidizing agent and reducing agent in the following equation. 3MnO2(s) + 4Al(s) 3Mn(s) + 2Al2O3(s)ORName a reducing agent that may be used to obtain manganese from manganese dioxide.

Answer: Reducing agent : Al Oxidation Agent : MnO2Q17: Give two example from everyday life situations where redox reactions are taking place.

Answer: Corrosion and Rancidity

Q18: In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode ?

Answer: In water (H2O), hydrogen and oxygen are present in the raito of 2:1 by volume.

Q19: Why should a magnesium ribbon be cleaned before burning in air?

Answer: Magnesium is a reactive metal. It combines with oxygen of air to form a layer of magnesium oxide on its surface. Hence, it should be cleaned with a sand paper before burning to remove the oxide layer formed on its surface.

Q20: Explain how respiration is an exothermic reaction.

Answer: During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. Hence, respiration is an exothermic process. C6H12O6(aq) + 6O2(aq) 6CO2(aq) + 6H2O(l) + energy (Glucouse)

Q21: What factors influence the rate of chemical reaction?

Answer: Following are the factors that can influence the rate of reaction: Nature of Reactants. e.g. Mg reacts faster in HCl than in acetic acid. Concentration of reactants Surface Area of reactants. E.g. Powdered CaCO3 reacts quickly than marble chips. Temperature Catalyst

Q22: Define Endothermic reaction.

Answer: The reactions in which heat is absorbed are called endothermic reactions. In such reactions heat is shown as one of the reactants. If exact amount of heat absorbed is known then this amount is written otherwise simply the word heat is written.E.g. N2(g) + 2O2(g) + heat 2NO(g) nitric oxide

Q23: A silver ware is kept in a solution of CuSO4 (aq). What change do you expect?Answer: No reaction. because Silver is less reactive than copper.

Q24(CBSE exam): Name one metal when placed in ferrous sulphate solution will discharge its green colour. Write a chemical equation and state the reasons also.

Answer: Potassium(K) is one example. K is more reactive than iron and will replace it. 2K + FeSO4 K2SO4 + Fe Potassium + Iron Sulphate Potassium Sulphate + Iron

Q25: Why do we apply paint on iron articles?Answer: Iron articles are painted to prevent them from rusting. Rusting is oxidation of iron in the presence of air and moisture. The paint layer cuts off the the contact of iron articles from moisture and air.

Q26(CBSE): A solution of a substance ''X'' is used for white washing(i) Name the substance ''X'' and write its formula(ii) Write the reaction of the substance ''X'' named in (i) above with water. Answer: (i) The substance ''X'' used for white washing is quick lime (calcium oxide). Its formula is CaO.(ii) When quick lime is mixed with water, the following reaction takes place:

CaO (s) + H2O(l) Ca(OH)2(aq) Quick Lime Water Slaked Lime (Calcium Oxide) (Calcium Hydroxide)

The white suspension of slaked lime when applied on the walls, combines with carbon dioxide (in air) forming a thin shining layer of calcium carbonate.

Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l)Slaked Lime Calcium Carbonate

Q27(CBSE): Why is it important to balance a chemical equation?Answer: The balancing of chemical equation is done to satisfy the law of conservation of mass, i.e. "total mass of all the products of reaction in a chemical reaction is equal the total mass of all the reactants".

Q28: What are the coefficients of the correctly balanced equation? ? Fe2O3 + ? CO ? Fe + ? CO2(a) 0, 2, 2, 3(b) 1, 3, 2, 3(c) 1, 2, 2, 2(d) 2, 6, 4, 3

Answer: (b) Ferric Oxide + Carbon Mono-oxide Iron + Carbon DiOxide

Q29: What are the coefficients of the correctly balanced equation? ? BaCl2 + ? Al2(SO4)3 ? BaSO4 + ? AlCl3 (aq)(a) 1, 1, 1, 2(b) 3, 2, 3, 2(c) 3, 1, 3,2(d) 2, 1, 1, 2

Answer: (c) 3 BaCl2 + 1 Al2(SO4)3 3 BaSO4 + 2 AlCl3 (aq)

Barium Chloride + Aluminium Sulphate Barium Sulphate + Aluminium Chloride

Q30(CBSE2011): What is the colour of FeSO4.7H2O crystals ? How does this colour change upon heating ? Give balanced chemical equation for the changes.

Answer: Hydrated ferrous sulphate crystals are green in colour. On heating, single reactant breaks down to give simpler products. This is a decomposition reaction.

Ferrous sulphate crystals (FeSO4.7H2O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases.

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Q31: Quick like (CaO - Calcium Oxide) reaction with water is regarded as exothermic. A student mixes these two products in a test tube and touches its side surface. Which of the following statement correctly describes the student's observation?

(a) The test tube becomes cold due to release of heat energy.(b) The test tube becomes hot due to release of heat energy.(c) The test tube becomes hot due to absorption of heat energy.(d) The test tube becomes cold due to absorption of heat energy.

Answer: (b) The test tube becomes hot due to release of heat energy.

Q32: The decomposition of vegetable matter into compost is an example of _____.(Choose the correct option). (a) endothermic reaction.(b) exothermic reaction.

Answer: (b) exothermic.

Q33(CBSE): Write a balanced chemical equation to represent the following reaction: Iron reacts with steam to form Iron(II,III) oxide and hydrogen gas.

Answer: 3Fe(s) + 4H2O(l) Fe3O4(s) + 4H2(g) Iron Water Iron Oxide Hydrogen

Q34(CBSE): Identify the substance oxidized, substance reduced, oxidising agent and reducing agent. MnO2 + 4HCl MnCl2 + 2H2O + Cl2

Answer: Substance Oxidised: HCl Substance reduced: MnO2 Reducing Agent: HCl Oxidising Agent: MnO2

Q35: Bromine gas (Br2) reacts with Sodium Carbonate (Na2CO3) in aqueous solution and gives sodium bromide (NaBr), sodium bromate (NaBrO3) and carbon-dioxide gas. How many number of sodium bromide molecules obtained in the balanced chemical equation.

Answer: From the question, we infer the unbalanced chemical equation is: Br2 + Na2CO3 NaBr + NaBrO3 + CO2

Balanced equation is: 3 Br2 + 3 Na2CO3 5 NaaBr + NaBrO3 + 3 CO2 It means 5 molecules of NaBr are obtained.

Q36: A numismatist (coin collector) has been collecting gold coins, silver coins and copper coins for a long time. One day he observed a black coating on silver coins and green coating on copper coins. What chemical process is responsible for these coatings. Also name the chemical formula of the black and green coatings.

Answer: The coating occurred due to a chemical process called corrosion. Black coating is due to deposit of Silver Sulphide (Ag2S). Green coating is due to formation of Copper Carbonate (CuCO3)(Note: Silver usually is corrosion resistant and does not oxidize. However presence of sulphur gases in atmosphere can react and cause sulphur-corrosion. )

Q37: Methane gas (CH4) when burns with oxygen (O2) gives carbon dioxide and water. Write the balanced chemical equation and provide the following information in terms of reactants and products in the equation.(a) no. of molecules (b) no. of moles(c) molar mass(d) total mass of reactants and productsWhat does statement (d) infer?

Answer: The balanced chemical equation is: CH4 (g) + 2 O2(g) 2H2O (l) + CO2(g) Methane + Oxygen water + carbon di-oxide ReactantsProducts

a. No. of moldeculesCH4 (g),O2(g) H2O, CO2(g)

b. no. of moles1 mole of CH4+ 1 mole of O2(g)2 moles of H2O + 1 mol of CO2

c. molar mass16g of CH4+ 64g of O2 44g of H2O + 36g of CO2

d.total mass80g 80g

CBSE Class 10 - Science - CH3 - Metals and Non-Metals Metals and Non-Metals

Q & A

Q1: List any five physical properties of metals.

Answer: Physical properties of metals are:1. Metals are usually hard (exceptions are: sodium and potassium). 2. These are sonorous. 3. These are lustrous. 4. Metals exhibit malleability and ductility. 5. Mostly they are solids (exception is mercury) 6. They exhibit high tensile strength. 7. These have high densities.

Q2: Are metals electronegative or electropositive?

Answer: Metals are electropositive i,e. they form cations by loosing electrons.

Q3: Define Malleability.

Answer: Malleability is the property of a metal, by which it can be beaten into thin sheets.

Q4: Name a metal which can be cut with a knife?

Answer: Sodium

Q5: Give examples of metals which are found in liquid form at room temperature.

Answer: Mercury and Gallium

Q6: Define ductility. Give two examples of metals that exhibit this property.Answer: Ductility is the property of a metal by which it can be drawn into thin wires. e.g. gold and silver.

Q7: Give an example of metal which is i. the best conductor of heat ii. the poor conductor of heat

Answer: (i) Silver (ii) lead

Q8: What are metalloids? Give examples of metalloids.

Answer: The elements that exhibit properties of both metals and non metals are called metalloids.e.g. bismuth, silicon, germanium, arsenic, antimony, tellurium and polonium

Q10: What are minerals?

Answer: The Inorganic elements or compounds of various metals found in nature, associated with their earthly impurities are called Minerals.

Q11: Can metals be extracted from all types of minerals?

Answer: No. Some minerals may have high percentage of metals while other do not.

Q12: What are ores?

Answer: Those minerals from which metals can be extracted profitably and conveniently are called Ores.

Q13: Define metallurgy.

Answer: The process of extracting metals from their ores followed by refining is known as metallurgy.

Q14: Give an example of non-metal which is lustrous.

Answer: Iodine

Q15: Give an example of a non-metal which is hard and has high melting point.

Answer: Diamond (allotrope of Carbon)

Q16: What is gangue and what is concentration?

Answer: Ores are usually associated with unwanted earthly matter called gangue (sand, clay etc.,) and the removal of this unwanted impurity is called concentration. The gangue has to be removed before the extraction of metals.

Q17: Why do potato chips manufacturers fill the packet of chips with nitrogen gas?

Answer: Nitrogen provides an inert atmosphere to prevent chips from getting oxidised.Nitrogen is an antioxidant which prevents oxidation of substances and that's why such type of food material is flushed with nitrogen in packs.

Q18: Name any non-metal which is found in liquid state at room temperature.

Answer: Bromine

Q19(KVS): You are given two statements a and b, select the correct inference from this:

a. Metals conduct heat.b. Diamond is the best conductor of heat.

i. Hence diamond is a metalii. Statement a is correctiii. Statements a and b is correctiv. None of the above

Answer: ii. Statement a is correct

Q20: Write differences between metals and non-metals based on physical properties.

Answer:SNo.Physical PropertyMetalsNon-Metals

1.Physical StateMetals are solid at room temperature. Exceptions are mercury, cesium and gallium.Non-metals generally exist as solids and gases, except Bromine which is a liquid

2.Melting and Boiling PointsMetals generally have high melting point and high boiling point. (exceptions are Na and K)Non-metals have low melting pt and low boiling point. (exceptions are C, Si and B)

3.HardnessMetals are generally hard. (exceptions are Na and k which can be cut by knife).Generally soft. (exceptions is diamond, the hardest substance)

4.LustreBright metallic lustre. Usually silvery white appearance except gold (yellow) and Cu (pinkish red)Lack Lustre (exceptions are iodine and graphite which are lustrous)

5.DensityHave high density (exceptions: Na, K and Ca. Na and K float on water)Generally low density except diamond which has high density.

6.MalleabilityMalleable Non-malleable

7.DuctilityDuctileNon-ductile

8.TenacityUsually have high tensile strength. (exceptions are Na, K and Hg which are non-malleable, non-ductile and have low tenacity).Lack tenacity.

9.BrittlenessUsually hard but not brittle. (exception is Zn which is brittle at room temperature.)Generally brittle.

10.ConductanceIn general metals are good conductors of heat and electricity. (exception is Bi)Usually non-conductors. (exceptions are graphite and gas carbon)

11.SolubilityUsually do not dissolve in liquids except by chemical reaction.Dissolve in liquid solvents.

12.Alloy and AmalgamUsually make alloys and amalgams.Do not form alloys except carbon which alloys with iron to form steel.

(In progress...)Class 10 - Science - CH4 - Carbon and Its Compounds (Q & A) Class 10 - Carbon and Its Compounds

cellulose(credits:wpclipart)

Q1. What is next homologue of C3H7OH is called?Answer: The next homologue of C3H7OH is called butanol C4H9OH.

Q2. What is the molecular formula of the alcohol which can be derived from propane?

Answer: Propane: CH3-CH2-CH3 or C3H8Alcohol obtained from propane is C3H7OH.

Q3. What is meant by the term functional group?

Answer: An atom or a group of atoms, which makes a carbon compound reactive and decides itsproperties. is called a functional group.

Q4. Give the names of the functional groups: (CBSE 2007) i) -CHO (ii -C=O

Answer: (i) Aldehydic group (ii) Ketonic group.

Q5. Give the names of the following functional groups: (CBSE 2007) i) OH (ii) COOH

Answer: (i) Alcoholic (ii) Carhoxylic.

Q6. Which functional groups always occur at the terminal position of a carbon chain?

Answer: Aldehydic group RCHO (R is tue alkyl group), and Carboxyl group RCOOH (R is the alkyl group).

Q7. Why a candle flame burns yellow, while a highly-oxygenated gas-fuel flame burns blue?

Answer: The most important factor determining color of the flame is oxygen supply and the extent of fuel-oxygen pre-mixing, which determines the rate of combustion and thus the temperature and reaction paths, thereby producing different color hues. In case of candle, it is an incomplete combustion and the flame temperature is not high. This gives a yellow flame. While a highly-oxygenated gas (e.g. ethyne) flame burns blue because of complete combustion raising a very high temperature.

Q8. Why is the reaction between methane and chlorine considered a substitution reaction? [CBSE 2008]

Answer: Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride. CH4+ Cl2 CH3Cl + HClWith the excess of chlorine, aH the four hydrogen atoms of methane are replaced by chlorine atoms to form carbon tetrachloride (CCl4). This reaction is considered as substitution reactions because hydrogen of methane is substituted by chlorine.

Q9: Why does Carbon form compounds mainly by covalent bonding?

Answer. Being tetravalent carbon atom, it is neither capable of losing all of its four valance electrons nor it can easily accept four electrons to complete its octet. Both of these are requirements of ionic bond formation and are energetically less favourable. Carbon completes its octet by sharing of electrons and hence covalent bonding is preferred.

Q10. Give a chemical test to distinguish between saturated and unsaturated hydrocarbons.

Answer. When saturated compounds are burnt in air, they give a clear (blue) flame but the burning of unsaturated compounds (akenes and alkynes) gives a sooty (yellowish) flame. Actually, saturated compounds contain comparatively less percentage of carbon which get completely oxidized by the oxygen present in air. On the other hand, the percentage of carbon in unsaturated compounds is more and it requires more oxygen to get completely oxidized that is not fulfilled by air. So due to incomplete oxidation they burn with a sooty flame.

Bromine-water test: Br2water is a brown coloured liquid.(a) Unsaturated hydrocarbons give addition reaction with Br2. So the colour of Br2-water gets decolourized. R-C=C-R + Br2 R-BrC-CBr-R(b) Saturated hydrocarbons do not react with Br2-water, so the colour of Br2.-water does not get decolourised.

Q11: What do you mean by Octane Rating?

Answer: Gasolines are rated on a scale known as octane rating, which is based on the way they burn in an engine. The higher the octane rating, the greater the percentage of complex-structured hydrocarbons that are present in the mixture, the more uniformly the gasoline burns, and the less knocking there is in the automobile engine. Thus, a gasoline rated 92 octane will burn more smoothly than one rated 87 octane.

Q12: Two compounds A and B react with each other in the presence of a dehydrating agent to produce an ester. Both react with Na to evolve hydrogen gas. On reaction with Na2CO3 only A evolves CO2. Identify the functional groups present in A and B giving reason for your answer.

Answer: Compound A contains COOH group while compound B contains OH group.

Since carboxylic acids and alcohols react with each other to form an ester, out of A and B, one is an alcohol and the other is a carboxylic acid. This is further strengthened by reaction of both with Na to evolve hydrogen gas.Only carboxylic acids react with Na2CO3 to evolve CO2, A contains COOH group while B contains OH group.

Following video posted on You tube by tutor vista nicely summarizes this chapter:

Q13:An organic compound 'X' is widely used as a preservative in pickles and has a molecular formula C2H2O2. This compound reacts with ethanol to form a sweetsmelling compound Y'. a. Identify the compound X b. Write the chemical equation for its reaction with ethanol to form compound Y. c. How can we get compound X back from Y? d. Name the process and write corresponding chemical equation. e. Which gas is produced when compound X reacts with washing soda? Write the chemical equation.

Answer:a. Compound X is ethanoic acid which gives and ester (Y) when reacts with ethanol.b. CH3COOH + CH3CH2OH CH3COOC2H5c. Esters gives back alcohol and carboxylic acid in the presence of acid or base.d. CH3COOC2H5 ---NaOH C2H5OH + CH3COOHe.CO2 gas is released. CH3COOH + Na2CO3 2CH3COONa + H2O + CO2

Q14(NCERT): What would be the electron dot structure of carbon dioxide which has the formula CO2?

Answer: Electron dot structure of CO2 is O=C=O

Q15(NCERT): What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint The eight atoms of sulphur are joined together in the form of a ring.)

Answer: S8 electron dot structure are in two forms:

Q16(NCERT): How many structural isomers can you draw for pentane?

Answer: There are three structural isomers of pentane:(i) Pentane CH3 CH2 CH2 CH2 CH3

(ii) 2-methyl Butane (iso-pentane) CH3CH2CHCH3 | CH3(iii) 2-2 dimethyl propane (neo-pentane) CH3 | CH3 CH CH3 | CH3

Q17(NCERT): What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

Answer: Two properties of carbon that attributes to its large family of carbon compounds are:1. Catenation: Ability to form chains with other atoms of carbon by covalent bonding. 2. Tetravalency: Valency = 4 i.e. it forms four covalent bonds with four other atoms.

Q18: What is Covalent bonding?

Answer: The chemical bonding occurs due to mutual sharing of electron pairs of two or more atoms of different elements is called covalent bonding. By mutual sharing of electron pairs atom attain noble gas configuration. e.g. In Hydrogen molecule (H2), the two H-atoms combine by covalent bonding (H-H).

Q19: What are Hydrocarbons? Give examples.

Answer: Compounds of carbon and hydrogen are called hydrocarbons. Methane, Ethane, Butane, ethyne, propene, benzene, petroleum products all are examples of hydrocarbons.

Q20(CBSE 2011): What are saturated hydrocarbons?

Answer:The hydrocarbons in which valency of carbon is satisfied by a single covalent bond are called saturated hydrocarbons. Alkanes like methane (CH4), ethane(C2H6), propane(C3H8) etc. are examples of saturated hydrocarbons. Saturated hydrocarbons will generally give a clean flame.

Q21(CBSE 2011): "Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame". Why?

Answer: Saturated hydrocarbons have only C-C and C-H single bonds and thus contain the maximumpossible number of hydrogen atoms per carbon atom. With sufficient oxygen, saturated hydrocarbons burn completely and give blue flame.CH4 + 2O2 CO2 + 2H2OUnsaturated hydrocarbons contain a carbon-carbon double bond (C=C) or triple bond (CC). Hence they contain less number of hydrogen than carbon. Unsaturated hydrocarbons undergoe incomplete combustion and give yellow flame along with black sooty(carbon). C2H4 + O2 CO2 + 2H2O + C(s)

Q22: What are isomers?

Answer: Compounds with identical molecular formula but different structures are called structural isomers. Organic compounds show a great level of isomerism. Isomers may be structural (due to difference in arrangement of C atoms forming chain) or stereo (due to arrangement of bonds in chain). With increase in number of carbon atoms in a molecular formula leads to increase in number of isomers. CCCC OR C-C-C | C

Q23(NCERT):Why do ionic compounds have high melting points?

Answer: Ions have strong electrostatic forces of attraction among them forming ionic compounds. It requires lot of energy to break these ionic bonds or forces. That's why ionic bonds have high melting points.

Q24: What are the characteristics of Homologue series?

Answer: Important characteristics of Homologue series are:1. Have same general formula. 2. Belong to same functional group. 3. Have general methods of separation. 4. Have similar chemical properties. 5. Show similar gradation of physical properties. e.g. boiling points of alcohol increase with increase in their molecular weights. 6. Similarly solubility decreases with increase in molecular weights.

Q25: What is the general formula of Alkanes?

Answer: CnH2n+2

Q26: What is a hetroatom? What is the hetroatom in alcohol functional group?

Answer: In a hydrocarbon chain, one or more hydrogen atoms can be replaced by other atoms according to their valencies. The element which replaces hydrogen in the chain is called a heteroatom.e.g. in alcohol (-OH) functional group, oxygen is the hetroatom.

. CBSE Class 10 - Science - CH2 - Acids, Bases and Salts

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MCQs, NCERT Solutions, Q & A

Q1: The most commonly used indicator in laboratory is(a) Methyl Orange(b) Litmus(c) Phenolphtalein(d) Universal Indicator

Answer: Universal Indicator

Q2: Olfactory indicators are:(a) Clove(b) Turmeric(c) Soap(d) Rose Petals

Answer: (a) Clove

Q3: An element common to all acids is(a) Chlorine(b) Nitrogen(c) Oxygen(d) Hydrogen

Answer: (d) Hydrogen

Q4: Metal carbonate on reaction with dilute acid release(a) CO2(b) CO(c) H2O(d) H2

Answer: (a) CO2

Q5 (Teachers FA manual): ln general, salts(a) are ionic compounds(b) contain hydrogen ions(c) contain hydroxide ions(d) turn litmus red

Answer: (a) are ionic compounds

Q6: On passing excess of CO2 gas in an aqueous solution of calcium carbonate, milkiness of the solution(a) persists(b) fades(c) deepens(d) disappears

Answer: (b) fades

Q7(FA manual): When magnesium and hydrochloric acid react, they produce(a) Oxygen and magnesium chloride(b) Chlorine and magnesium oxide(c) Hydrogen and magnesium chloride(d) Hydrogen and magnesium oxide

Answer: (c) Hydrogen and magnesium chloride

Q8: Dissolution of acid or base in water is(a) Exothermic(b) Endothermic(c) Violent(d) None of these

Answer: (a) ExothermicQ9: Water contains more H+ ions than OH- ions. In this case, water is(a) neutral(b) basic(c) acidic(d) cannot say.

Answer: (c) acidic

Q10: When an acid reacts with a base what compounds are formed?(a) water only (b) metal oxides only(c) a salt only (d) a salt and water

Answer: (d) a salt and water

Q11: Which of the following is a property of an acid?(a) slippery feel(b) non-reactive(c) sour taste(d) strong color

Answer: (c) sour taste

Q12: On diluting an acid concentration of H+ per unit volume(a) increases(b) decreases(c) remains unaffected(d) depends on type of acid used.

Answer: (b) decreases

Q13: What is pH?(a) the positive logarithm of the hydroxide ion concentration(b) the positive logarithm of the hydrogen ion concentration(c) the negative logarithm of the hydroxide ion concentration(d) the negative logarithm of the hydrogen ion concentration

Answer: (d) the negative logarithm of the hydrogen ion concentration

Q14: Tartaric acid is the constituent of(a) bleaching powder(b) baking powder(c) washing powder(d) plaster of paris

Answer: (b) baking powder

Q15: A solution turns blue litmus red. Its pH value is likely to be(a) 4(b) 7(c) 9(d) 12

Answer: (a) 4

Q16: What is the name of H2SO3?(a) Sulphuric Acid(b) Sulphurous Acid(c) Sulphite Acid(d) Hydrogen Sulphide.

Answer: (b) Sulphurous Acid

Q17: Which gas is produced by reaction of base with metal ?(a) Carbon dioxide(b) Dioxygen(c) Dihydrogen(d) Dinitrogen

Answer: (c) Dihydrogen

Q18: Acid + Metal-oxide ?(a) Base + Water(b) Salt + Water(c) Base + Salt(d) Metal + Salt

Answer: (b) Salt + Water

Q19: Which of the following is a weak acid?(a) Hydrochloric Acid(b) Nitric Acid(c) Acetic Acid(d) Sulphuric Acid

Answer: (c) Acetic Acid

Q20: An indicator is what type of compound?(a) reducing agent(b) strong base or acid(c) weak base or acid(d) salt

Answer: (c) weak base or acid

Q21: Which of the following is strong acid ?(a) Acetic acid(b) Citric acid(c) Nitric acid(d) Oxalic acid

Answer: (c) Nitric acid

Q22: Name the organic acid present in tomato(a) Tartaric Acid(b) Malic Acid(c) Lactic Acid(d) Oxalic Acid

Answer: (d) Oxalic Acid

Q23: Fill in the blanks.(a) Turmeric, clove, rose petals are ______ _____ .(b) Acids ______ _______ bases to form ________ and water.(c) The term pH was coined by _______ .(d) Turmeric turns _____ _______ in basic medium.(e) ________ ________ is used in softening water.(f) String acids show ______ ionisation while weak acids show _______ ionisation.(g) Calcium Sulphate hemihydrate is popularly known as _____ ___ _____.(h) Acids contain the hydrogen (H+) as the only ______ _______.(i) Bases contain the Oxide (O2-) or hydroxide (OH-) radical as the only _______ radical.

Answer:(a) Olfactory indicators(b) reacts with, salt (c) Srensen(d) deep brown(e) Washing Soda(f) more, less(g) Plaster of Paris(h) positive radical(i) negative Q24: List the organic acid present in the following objects:(a) Citrus Fruits (lemon, orange)(b) Sting of bees and ants(c) Rancid butter(d) Tamarind, grapes, apples(e) Apples(f) Gastric juice(g) Vinegar(h) Fats(i) Urine(j) Sour milk, curd

Answer: (a) Citrus Fruits (lemon, orange): Citric acid(b) Sting of bees and ants: Formic acid(c) Rancid butter: Butryic acid (d) Tamarind, grapes, apples : Tartaric acid(e) Apples: Malic acid(f) Gastric juice: Hydrochloric acid(g) Vinegar: Acetic acid(h) Fats: stearic Acid(i) Urine: Uric Acid(j) Sour milk, curd: Lactic acid

Q25: State true () or false ()(a) Heat is evolved during ionisation.(b) Solution of glucose in water produces ions.(c) Dry ammonia has no effect on litmus paper.(d) Higher is the concentration of H(aq), lower is the pH value.(e) The concentration of aqueous solutions of acid, base and salt are generally expressed in molarity.(f) pH of a solution can vary from 0-14.(g) HC1 is a weak acid.(h) NaOH is a strong base.(i) Curd is alkaline in comparison to fresh milk.(j) pH = + log10[(H3O-](k) Distilled water does not conduct electricity.(l) Analgesics helps to relieve acidity.

Answer:(a) Heat is evolved during ionisation. - True()(b) Solution of glucose in water produces ions. False ()(c) Dry ammonia has no effect on litmus paper. (True)(d) Higher is the concentration of H(aq), lower is the pH value. True()(e) The concentration of aqueous solutions of acid, base and salt are generally expressed in molarity.True()(f) pH of a solution can vary from 0-14.True()(g) HC1 is a weak acid. False ()(h) NaOH is a strong base.True()(i) Curd is alkaline in comparison to fresh milk.False ()(j) pH = + log10[(H3O-] False ()(k) Distilled water does not conduct electricity. True()(l) Analgesics helps to relieve acidity. False ()

Q26: Identify which of the following chemical formulas is acid, base or salt. Write their corresponding chemical names also.(a) HCl(b) NaOH(c) NaCl(d) Ca(NO3)2(e) Ca(OH)2(f) HNO3(g) NH4OH(h) (NH4)2SO4(i) CuO(j) H2SO4(k) CuCO3(l) H2CO3(m) MgO(n) Mg3(PO4)2

Answer:(a) HCl - Hydrochloric Acid (b) NaOH - Sodium Hydroxide - Base(c) NaCl - Sodium Chloride - Salt(d) Ca(NO3)2 - Calcium Nitrate - Salt(e) Ca(OH)2 - Calcium Hydroxide(f) HNO3 - Nitric Acid (g) NH4OH - Ammonium hydroxide - Base(h) (NH4)2SO4 - Ammonium sulphate - Salt(i) CuO - Copper Oxide (j) H2SO4 - Sulphuric Acid(k) CuCO3 - Copper Carbonate(l) H2CO3 - Carbonic acid(m) MgO - Magnesium Oxide(n) Mg3(PO4)2 - Magnesium Phosphate

Q27: You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer: The colour of red litmus paper changes to blue indicates that the chemical is a base. If there is no change in colour, then it is either acidic or neutral. We can easily identify a base.1. Mark the three test tubes as A, B, and C. 2. Take a drop of the solution A and put it on the red litmus paper. Repeat the same process iwth solution B and C. 3. If any of them changes colour to blue, then it is a base.And remaining two are acid and neutral. 4. Now take a drop from the identified base and mix it with a drop taken from the remaining two solutions separately. 5. Check the drops of the mixtures on red litmus paper. 6. If the colour of red litmus turns blue, then the second solution is neutral. If it does not change colour, then the second solution is acid. This is because acidic and basic solutions neutralize each other.

Q28: Why should curd and sour substances not be kept in brass and copper vessels?

Answer: Curd and sour substances are acidic by nature. e.g. curd contains lactic acid. When these substances are kept in metal containers like brass and copper, metal react with acid and liberate hydrogen gas and other harmful substances, which may spoil these substances.

Q29: Why vinegar is used in pickling?

Answer: Vinegar contains an organic acid called acetic acid (CH3COOH) which prevents the growth of micro organisms. Therefore it is used in pickling.

Q30: Why phenolphthalein is considered acid base indicator?

Answer: It is because phenolphthalein turns pink in basic solution whereas it remains unaffected in acid or neutral solutions. It is able to differentiate between acid (colouless) and base (pink colour).

Q31(NCERT): Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Answer: Hydrogen gas is liberated when an acid reacts with a metal.Take few pieces of zinc (Zn) granules in a delivery tube. Add 5ml of hydrochloric acid (HCl). White fumes will rise. Pass the gas to a soap solution or collect it in a balloon (as shown in the following video). The gas collected is Hydrogen gas. Since H2 gas has lower density as compared to air, the balloon will float in air.

Zn (s) + 2HCl (aq) ZnCl2(s) + H2 (g)

You can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the balloon (or soap bubbles).

Q32(NCERT): Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Answer: Since CO2 gas is liberated and the salt obtain has metal Ca, it implies the reactant metal compound shall be a carbonate i.e. CaCO3 The chemical equation is:

CaCO3 (s) + 2HCl (aq) CaCl2 (s) + CO2 (g) + H2O (l)Calcium Carbonate + Hydrochloric Acid Calcium Chloride + Carbon Dioxide + Water

Q33(NCERT): Why do HCl, HNO3 , etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Answer: As aqueous solution, HCl and HNO3 dissociate into H+ and Hydronium (H3O+) ions. HCl (aq) H+ + Cl- H+ + H2O H3O+

Although glucose and alcohol contain hydrogen, as aqueous solution, they do not dissociate into ions and do not exhibit acidic character.

Q34(NCERT): Why does an aqueous solution of an acid conduct electricity?

Answer: The aqueous solution of an acid contains H+ and Hydronium (H3O+) ions. Since ions carry extra charge and are able to conduct electricity.

Q35: Why should acids be handled with care?

Answer: Acids have burning effect on our skin. They are corrosive to living beings. Proper care must be taken while handling acids in laboratory.

Q36: Why does dry HCl gas not change the colour of dry litmus paper

Answer: Dry HCl gas does not form H+ions. It does not show its acidic character. When in the aqueous solution, an acid ionizes to form H+ions. In this case, neither HCl is in an aqueous form nor the litmus paper is wet, therefore, the colour of the litmus paper does not change.

Q37: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer: When diluting, the acid should always be added slowly to water and in small amounts. Adding water to an acid is an exothermic process, it can cause uncontrolled boiling and splashing. That's why it is recommended that the acid should be added to water and not water to the acid.

Q38: What is an amphoteric substance?

Answer: A substance is said to be amphoteric if it can behave either as an acid or as abase. Water is the most common amphoteric substance.

Q39: On the basis of origin, how acids are classified?

Answer: On the basis of origin, acids are classified as:1. Organic acids 2. Inorganic or Mineral acids Q40: What are organic acids? Give two examples

Answer: Acids obtained from living beings (plants and animals) are called organic acid.e.g. citric acid present in fruits like lemon, oxalic acid in tomato etc.

Q41: What are mineral acids? Give two examples

Answer: In general acids obtained from minerals or non-living things are called mineral or inorganic acids. Examples are: Sulphuric acid (H2SO4) Nitric Acid (HNO3) Q42: What is the chemical name of Bleaching powder? How it is prepared? List its uses.

Answer:Chemical Name of Bleaching Powder: Calcium OxychlorideChemical Formula: CaOCl2Preparation: It is prepared by passing chlorine gas through dry slaked lime. Ca(OH)2+ Cl2 CaOCl2 + H2O Slaked Lime + Chlorine Bleaching Powder + Water

Uses:1. As bleaching agent in textile industry. 2. As disinfectant in water purification. 3. In paper industry to bleach wood pulp. Q43: Which acid is used in Cola to give it a biting sharp taste?

Answer: Phosphoric acid.

Q44: What is gypsum?

Answer: Plaster of Paris reacts with water to give a hard mass called gypsum. (CaSO4)2. H2O (s) + 3 H2O (l) 2CaSO4.2H2O (s) Plaster for Paris + Water Gypsum

Q45 Define Dilution.

Answer: Mixing an acid or base with water results in decrease in the concentration of ions (H3O+/OH) per unit volume. Such a process is called dilution and the acid or the base is said to be diluted.

Q46(CBSE 2010): Tooth enamel is one of the hardest substance in our body. How does it undergo damage due to the eating of chocolates and sweets? What should we do to prevent it?orQ: Why does tooth decay start when the pH of the mouth is lower than 5.5?

Answer: Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium phosphate is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar (due to chocolates and sweets) and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food.

Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

. Class 10 - Science - CH13 - Magnetic Effects of Electric Current Magnetic Effects of Electric Current

Earth's Magnetic Field (computer simulation)credits: wikipedia

MCQs, Q & A from CBSE Papers

Q1: The two poles in a magnet have(a) equal pole strength.(b) unequal pole strength.(c) can be same or different(d) None of these

Q2:A magnet AB is broken into two pieces. What is the polarity of A, B, C and D?

(a) A, D: North & B,C: South(b) A, B: North & C,D: South(c) A,C: North & B,D: South(d) A,D: South & B,C: North

Q3: Magnetic field lines:(a) form closed curves(b) cannot intersect(c) are crowded near poles(d) All of these

Q4: The correct field lines are:

Q5:Who had first observed the magnetic effect of an electric current first ?(a) Faraday(b) Oersted(c) Volta(d) Ampere

Q6(NCERT): The magnetic field inside a long straight solenoid-carrying current(a) is zero(b) decreases as we move towards its end(c) increases as we move towards its end(d) is the same at all points

Q7: With the help of which law the direction of a magnetic field can be decided ?(a) Faraday's law(b) Fleming's right hand rule.(c) Right hand thumb rule(d) Fleming's left hand rule.

Q8(NCERT): Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)(a) mass(b) speed(c) velocity(d) momentum

Q9(NCERT): Which of the following correctly describes the magnetic field near a long straight wire?(a) The field consists of straight lines perpendicular to the wire.(b) The field consists of straight lines parallel to the wire.(c) The field consists of radial lines originating from the wire.(d) The field consists of concentric circles centred on the wire.

Q10: What is the field line of a magnetic field passing through the centre of current carrying circular ring ?(a) Circular(b) Straight line(c) Ellipse(d) Magnetic field is zero at center.

Q11: Frequency of AC in India is(a) 50 Hz(b) 60 Hz(c) 110 Hz(d) 220 Hz

Q12: As we move away from a current carrying conductor, the spacing between the magnetic lines of force(a) decreases(b) increases(c) remains at equal distances(d) none of these

Q13(NCERT): A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is(a) towards south(b) towards east(c) downward(d) upward

Q14: Whose magnetic field is like a magnetic field of a bar magnet?(a) Current carrying wire(b) Current carrying ring.(c) Current carrying solenoid(d) Current carrying rectangular loop

Q15(NCERT): A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each(a) two revolutions(b) one revolution(c) half revolution(d) one-fourth revolution

Q16: From which of the following case, the current in the loop will not be induced ?(a) The loop is moved in the direction of the magnet.(b) The magnet is moved in the direction of the loop.(c) The loop and magnet are moved in the opposite direction with the same speed.(d) The loop and magnet are moved in one direction with the same speed.

Q17(NCERT): The phenomenon of electromagnetic induction is

(a) the process of charging a body.(b) the process of generating magnetic field due to a current passing through a coil.(c) producing induced current in a coil due to relative motion between a magnet and the coil.(d) the process of rotating a coil of an electric motor.

Q18(NCERT): The device used for producing electric current is called a(a) generator.(b) galvanometer.(c) ammeter.(d) motor.

Q19(NCERT): The essential difference between an AC generator and a DC generator is that(a) AC generator has an electromagnet while a DC generator has permanent magnet.(b) DC generator will generate a higher voltage.(c) AC generator will generate a higher voltage.(d) AC generator has slip rings while the DC generator has a commutator.

Q20(NCERT): At the time of short circuit, the current in the circuit(a) reduces substantially.(b) does not change.(c) increases heavily.(d) vary continuously.

Answers:1: (a) equal pole strength.2: (c) A,C: North & B,D: South3: (d) All of these4: (a)5: (b) Oersted6: (d) is the same at all points7: (b) Fleming's right hand rule.8: (c) velocity and (d) momentum9: (d) The field consists of concentric circles centred on the wire.10: (b) Straight line11: (a) 50 Hz12: (b) increases13: (d) upward [hint: use Fleming's left hand rule]14: (c) Current carrying solenoid 15: (c) half revolution16: (d) The loop and magnet are moved in one direction with the same speed.17: (c) producing induced current in a coil due to relative motion between a magnet and the coil.

18: (a) generator.19: (d) AC generator has slip rings while the DC generator has a commutator.20: (c) increases heavily.

Q21(CBSE 2010): What does the direction of thumb indicate in the right-hand thumb rule?

Answer: Motion of the conductor.

Q22(CBSE ): Why does the acceleration of a bar magnet decreases while falling through a solenoid, connected to a closed circuit?

Answer: The induced current will exert an opposing force which will reduce the acceleration of falling bar magnet.

Q23(CBSE): Can two magnetic lines of force ever interact? Justify your answer. orQ(NCERT): Why dont two magnetic lines of force intersect each other?

Answer: No. Two magnetic lines of force never interact. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.

Q24(CBSE 2010): What will be the frequency of an alternating current, if its direction changes after every 0.01 s?

Answer: If ac current changes its direct in 0.1s, it means it completes its cycle in 0.2s(0.1s+0.1s). Frequency = 1/Time period = 1/0.02 = 50Hz.

Q25(CBSE 2010): AB is a current carrying conductor in the plane of the paper as shown in figure. What are the directions of magnetic field produced by it at points P and Q? Given r1 > r2, where will the strength of the magnetic field be larger?

Answer: To know the direction of magnetic field produced by current passing through a conductor, we can apply 'Right Hand Thumb Rule' or Maxwell Corkscrew rule.At point P, the magnetic field lines enter into the paper(screen). At point Q, the field lines are coming out of paper (screen)

Magnetic field follows inverse square law i.e. a magnetic field decreases inversely at a distance while moving away from the conducting wire.Since r1 > r2, magnetic field is larger at Q than P.

Q26: Name two sources of direct current and alternating current.

Answer: DC source: dry cell, solar cell. AC source: AC dynamo, turbines

Q27: What will happen to magnetic field due to a circular coil carrying electric current, if the number of turns of the coil is doubled.

Answer: The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it. If the number of turns in the circular coil is doubled, the field produced will also get doubled as that produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to each turn then just adds up.

Q28(CBSE 2011): Why does a current carrying conductor experiences a force when it is placed in a magnetic field? State Flemings left hand rule.

(Note: What happens when two bar magnets are kept close to each other. They either repel or attract. It happens because the magnetic field lines of the two interact each other. The answer for the above question is also similar).

Answer: The current carrying conductor produce magnetic field. When this conductor is placed in a magnetic field, it experiences a force due to mutual interaction of these two magnetic fields.

Fleming's Left Hand Rule(credits:wikipedia)

Fleming's Left hand rule states, "When an electric current (I) flows in a wire, and an external magnetic field (B) is applied across that flow, the wire experiences a force (F) perpendicular both to that field and to the direction of the current flow."

It can be represented by the left hand. Stretch the thumb, forefinger and middle finger: of your left hand mutually perpendicular to each other such that the fore finger points in the direction of magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

Flemings' Left Hand rule for electric motors Flemings' Right Hand rule if for electric generators.

See also nice tutorial with beautiful graphics on Motors and Generator by Florida State University.

Q29(NCERT/CBSE 2010/2011): List the properties of magnetic lines of force.or

Q(CBSE 2011): (i) What is the direction of magnetic field lines outside a bar-magnet ?(ii) Why two magnetic field lines cannot intersect each other ?(iii) What is indicated by crowding of magnetic field lines in a given region ?

Answer: Properties of magnetic lines of force are:1. The imaginary lines which represent the direction of magnetic field, are known as magnetic lines of force. 2. Magnetic lines of force are closed curves. Outside the magnet their direction is from north pole to south pole and inside the magnet these are from south to north pole. 3. They neither have origin nor end. 4. These lines do not intersect, because if they do so then it would mean two value of magnetic field at a single point, which is not possible. 5. At the poles of the magnet the magnetic field is stronger because the lines of force there arecrowded together and away from the poles the magnetic field is weak. Q30: When the current flows in a coil in anti-clockwise direction, what pole does it create?

Answer: North Pole

Q31(CBSE 2011): What is the advantage of a.c. over d.c.?

Answer: The advantage of AC over DC is that electric power can be transmitted over long distances without much loss of energy.

Q32: What does MRI stands for?Answer: Magnetic Resonance Imaging.

Q33: What colour conventions are used in domestic electrical wiring to indicate:(i) live wire(ii) neutral wire (iii) earth wire

Answer: (i) live wire - red(ii) neutral wire - black(iii) earth wire - green

Q34: State the principle on which an electric generator works?

Answer: It works on the principle of electromagnetic induction. It converts mechanical energy into electrical energy.

Q35: (i) What is a commutator?(ii) In an electric motor which part act as commutator?(iii) How does it help?

Answer:(i) A device that reverses the direction of flow of current through a circuit is called a commutator.

(ii) In electric motors, the split ring acts as a commutator.

(iii) The reversal of current also reverses the direction of force acting on the two arms and generates a torque. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

Q36: (i) What is an armature? What is its advantage?(ii) What are the advantages of electromagnet over permanent magnet?

Answer: The soft iron core, on which the coil is wound, plus the coils, is called an armature. It is used in electric motors to act as an electromagnet. The armature (electromagnet) enhances the power of the motor.(ii) The advantages are:1. You can turn the electromagnet by switching ON or OFF the current. 2. You can reverse the poles of the electromagnet by reversing the direction electric current flow in the coil. 3. The magnetic field strength can be changed by changing the amount of current in the coil. 4. An electromagnet can easily be made more powerful than a permanent magnet. Q37: Define electromagnetic induction. What are the different ways to induce current in a coil?

Answer: The process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction.

We can induce current in a coil by applying any of the following: (i) by moving it in a magnetic field (ii) by changing the magnetic field around it.

Q38(HOTS): When a proton moves in a uniform magnetic field, why does the momentum change but its kinetic energy does not change? (Revisit MCQ Q8 above).

Answer: The magnetic force exerted will be perpendicular to the direction of motion of the proton. As we know when when force acting is perpendicular to the direction of moving charge, work done will be zero. It means kinetic energy does not change. The force is able to change the direction (velocity) of the proton but not its speed (magnitude). Thus momentum and velocity changes.

Q39: Is magnetic field vector or scalar quantity?

Answer: Magnetic field is a vector quantity. It has both magnitude and direction.

Q40: Can a 5A fuse be used in wire carrying 15 A current? Why?

Answer: Since the current withdrawn in the electric circuit is 15A, the fuse will blow frequently and remain ineffective.

Q41(CBSE 2011/NCERT): An electric oven of 2 kW power rating is operated in a domestic electric circuit that has a current rating of 5A. If the supply voltage is 220V, what result do you expect ? Explain.

Answer: Given, Power of the oven (P) = 2kW = 2 103 W Voltage supplied (V) = 220V Current (I) = ? A Power = V I I = P/V = 2 103/ 220 = 9.09 ASince the domestic electric circuit has a current rating of 5A, the flow of 9.09 A by the Oven exceeds the safe limit. Here, fuse will blow and break the circuit.

Q42: A current flows from the wire wound around an iron nail as shown in the figure below. Where is the North Pole and South Pole?

Answer: You may use right-hand rule i.e. if fingers of right hand curl in the direction of the current, thumb points towards the North pole. Top one will be South Pole and bottom face will be the North Pole.

Q43(CBSE): What are the different ways to strengthen an electromagnet?

Answer:1. Can add second battery to increase the amount of current. 2. Add more number of turns in the coil. In addition, an electromagnet also depends on the type of core used. Type of material, shape, size and winding pattern of the coil also control the shape and strength of the magnet field of an electromagnet.

Q44: A current of 5A is flowing through a conductor AB. Will the current be induced in the circular wire of give radius 1m?

Answer: Since a steady current of 5A is flowing through the conductor, no current or emf will be induced in the circular wire.class 10 - Numericals on Light Reflection and Refraction

Numerical Problem on Light Reflection and Refraction (More numerical and questions at this page) Q1: How fast does the light travel in a glass of refractive index 1.5?

Answer:By Snell's law, refractive index (n) is the ratio of i.e.

Q2:When a bright object is placed 10 cm away from a concave mirror, its real image is formed at a distance 40cm from the mirror. What is the focal length of the mirror?

Answer:

Q3: If the angle of incidence of a ray of light falling on the glass surface is 30 and the angle of refraction is 19. what is the refractive index of glass?

Ans: angle of incidence i = 30 angle of refraction r = 19 refractive index n = sin i/sin r = sin 30/sin 19 n = .5/.3256 = 1.535 ....(ans)

Q4: If a child crawls towards a mirror at a rate of 0.20 m/s, then at what speed will the child and her image come nearby to each other?

Ans: In 1 sec, the child moves towards the mirror by a distance of 0.20 meters. In the same second, her image also moves 0.20m closer.Therefore, the child and her image comes closer to each other by 0.40m per second.

Q5: How many images will you see when two plane mirrors are perpendicular to each other?Ans: The answer is three. You may see practically as shown in the figure. You may follow the link on multiple reflections to see more such images.

For two mirrors placed at any angle, the number of images formed by the mirrors can be determined by:

N = (360/ ) - 1

where is the angle between the mirrors and N is the number of images formed. For parallel mirrors = 0, hence N = . (You may have seen this effect in barber shops).

Q6: A converging lens has a focal length of 15cm. An object is placed 60cm from the lens. Determine the image.

Ans: Object Distance is u = -60cm focal length f = 15 cm

Lens formula is: 1/v - 1/u = 1/f 1/v = 1/15 + (-1/60) = 1/20 v = 20 cmThe image is real (+ve v) and is formed on the other side of the lens.The magnification is: m = 20/-60 = -1/3The -ve sign of m tells that the image is inverted. The magnitude of m (magnification) is less than one, thus image formed is of reduced size.

Q7: What is the focal length of a lens that produces a real image three times as large as the object if the distance between image and object is 1.0m?

Ans: magnification m = 3 Let u be the object distance, the image distance will be v = 1-u Since image is real, we can assume it is a convex lens. m = 3 = v/u = (1-u)/u u = -025cm and v = 0.75cm 1/v - 1/u = 1/f f = 18.75cm

Q8(*): At what value of the angle of incident 1 is a beam of light reflected from the surface of water perpendicular to the refracted beam? Assume n is the refractive index of the refracting medium.

Answer: Let us try to draw a ray diagram to understand the problem.

Let XY be the plane which separates the two media. The incident ray AO gets reflected partly as OB and gets refracted as ray OC. NOM is normal to the plane.

incident angle AON = 1reflected angle NOB = 2refracted angle COM = 3

Since COB = /2 ...(given)1 = 2 ...(2nd law of reflection) This gives 2 = /2 - 1

According to Snell's law (2nd law of refraction),n = sin i/sin r = sin 1/sin 2 n = sin 1/sin ( /2 - 1)} n = sin 1/ cos 1$ n = tan 11 = tan-1 n

Q 9: Using mirror formula, compute the position of the object placed in front of a concave mirror of focal length f so that the image formed is of same size of the object. Answer: In this case, magnification m = 1, since image size = object size (given).

Q10: Water has refractive index = 1.33 and air has refractive index = 1.00. Find the critical angle for a water-air boundary.

Answer: Critical angle is considered when a ray of light travels from denser medium to refractive medium.See the figure,

the angle of incidence i = c and r = 90Applying snell's law 1 sin c = 2 sin 90 1.33 sin c = 1.00 sin 90 sin-1 c = 0.752 c = 48.7

Q11 (NCERT): Find the focal length of a convex mirror whose radius of curvature is 32 cm.

Answer: Given, radius of curvature = 32 cmFocal Length = radius of curvature / 2 = 32 /2 = 16 cm

Q12(NCERT): A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located?

Answer: Given mirror = concave mirrorDistance of the object from mirror = - u = - 10 cmDistance of the image from the concave mirror = v?

Magnification (m) = -3

m = -v/u -3 = -v/-10 cm v = -3 10 = -30 cmThus image is formed 30 cm from pole in front of the concave mirror (-ve sign tells that image formed is on the same side of the object).

(More numerical and questions at this page)Showing posts with label 10th Electricity and Effects. Show all posts Showing posts with label 10th Electricity and Effects. Show all posts08 April 2013CBSE Physics Numerical based on chapter - Electricity & its effects For (Class X) NUMERICAL - Electricity and its effects For (Class X)

1. 16. A resistance of 6 ohms is connected in series with another resistance of 4 ohms. A potential difference of 20 volts is applied across the combination. Calculate the current through the circuit and potential difference across the 6 ohm resistance.2. Calculate the number of electrons constituting one coulomb of charge per second through any cross section of a conductor.3. How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V ?4. How much energy is given to each coulomb of charge passing through a 6 V battery ?5. Calculate the work done in moving a charge of 5 Coulombs from a point at a potential of 210 Volts to another point at 240 Volts.7. When a particle of charge 10 C is brought from infinity to a point P, 2.0 mJ work is done by the external forces. What is the potential at P ?9. How many electrons pass through a lamp in one minute if the current be 200 mA?10. Calculate the current supplied by a cell if the amount of charge passing through the cell in 4 seconds is 12 C ?11. A 2 Volt cell is connected to a 1 resistor. How many electrons come out of the negative terminal of the cell in 2 minutes?12. a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 ?b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 ?13. The potential difference between the terminals of an electric heater is 60 Volts when it draws a current of 4 Ampere from a source. What current will the heater draw if the potential difference is increased to 120 Volt.14. A torch bulb when cold has 1 resistance. It draws a current of 0.3 Ampere when glowing from a source of 3 V. Calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance. 15. A current of 0.2 Ampere flows through a conductor of resistance 4.5 . Calculate the potential difference at the ends of the conductor. Paper for formative assesmentsRelated search and topics10th science physics Electric current and its effects Formative AssessmentsGuess Paper SA-1- 2011 - X -Science-Electricity and its effects10th science physics Electric current and its effects notes10th science physics Electric current and its effects Solved questions (1-2 marks)10th science physics Electric current and its effects Test PaperNUMERICAL - Electricity & its effects For (Class X unsolved)Solved Electricity numerical for class 10Current Electricity Numerical solvedMCQ physics 10th Chapter Electric current and its effectsElectric current and its effects: An Introduction To Electrical Power And EnergyElectric current and its effects: An Introduction To Electric Potential and Potential DifferenceQUESTION BANK Class X Physics (Electricity)CBSE PHYSICS : 10th Electric Current & and Its Effect Multiple choice questionsELECTRIC CURRENT AND CIRCUIT+ Revision NotesYou might also like: NUMERICAL - Electricity & its effects For (Class X) X Electric Current and Its Effect CBSE -1 Most Important Questions Guess Paper SA-1- 2011 - X -Science-Electricity and its effects Heating Effect of Electric Current and Electrical Power Linkwithin Posted by J Sunil at Monday, April 08, 2013 0 comments Email This BlogThis! Share to Twitter Share to Facebook Labels: 10th Electricity and Effects, 10th Physics 25 May 2012Sadhana Devi Vidyapith: Physics : Class X Chapter: ELECTRICITY Assignment ... Physics : Class X Chapter: ELECTRICITY Assignment 2012-13

ASSIGNMENT -1, (2012-13) By JSUNIL Sub. Physics, Class - X Chapter -ELECTRICITY One mark questions 1. Define the term electric current.

2. Define the term resistivity of a material.

3. How is a Voltmeter connected in the circuit to measure the potential difference between two points?

4. You have two metallic wires of resistances 6 ohm and 3 ohm. How will you connect these wires to get the effective resistance of 2 ohm?

5. If the distance between two electric charges is doubled, how much will the force exerting between them change to? Two marks questions

6. State Ohms law. The resistance of a conductor is 1. What is meant by this statement?

7. Why are coils of electric toaster made of an alloy rather than a pure metal? 8. Why is...Read more

Related search and topics10th science physics : Termology : Electric current and its effects10th science physics: Electric current and its effects Formative AssessmentsGuess Paper SA-1- 2011 - X -Science-Electricity and its effects10th science physics Electric current and its effects notes10th science physics Electric current and its effects Solved questions (1-2 marks)10th science physics Electric current and its effects Test PaperNUMERICAL - Electricity & its effects For (Class X unsolved)Solved Electricity numerical for class 10Current Electricity Numerical solvedMCQ physics 10th ChapterElectric current and its effectsElectric current and its effects:An Introduction To Electrical Power And EnergyElectric current and its effects: An Introduction To Electric Potential and Potential DifferenceQUESTION BANK Class X Physics (Electricity)CBSE PHYSICS : 10th Electric Current & and Its Effect Multiple choice questionsELECTRIC CURRENT AND CIRCUIT+ Revision Notes10th Solved Science Sample paperYou might also like: CBSE Physics Numerical based on chapter - Electricity & its effects For (Class X) Guess Paper SA-1- 2011 - X -Science-Electricity and its effects NUMERICAL - Electricity & its effects For (Class X) X Electric Current and Its Effect CBSE -1 Most Important Questions Linkwithin Posted by J Sunil at Friday, May 25, 2012 0 comments Email This BlogThis! Share to Twitter Share to Facebook Labels: 10th Electricity and Effects 30 April 2012X MCQ based on Chapter Electricity MCQ OF ELECTRICITY

1.The rate of flow of an electric charge is known as :

(a) electric potential (b)electric conductance(c)electric current (d)none of these

Ans : (c)electric current

2.The SI unit of electric current is :

(a)ohm (b)ampere (c)volt (d)faraday

Ans :(b)ampere

3.The instrument used for measuring electric current is :

(a)ammeter (b)galvanometer (c)voltmeter (d)potentiometer

Ans :(a)ammeter

4.The amount of work done in joules, when one unit electric charge moves from one point to another point in an electric circuit is called :

(a)electric current (b)electric resistance (c)electric conductance (d)potential difference

Ans :(d)potential difference

5.The unit of potential difference is :

(a)volt (b)ohm (c)ampere (d)faraday

Ans :(a)volt

6.The relation between potential difference (V) and current (I) is :

(a)V I2 (b) V 1/I (c) V2 I (d) V I

Ans :(d) V I

7.The relation between potential difference (V) and current (I) was discovered by :

(a)Newton (b) Ampere (d) Volta

Ans : (c) Ohm

8.The obstruction offered by material of conductor to the passage of electric current is known as :

(a)Resistance (b) Conductance (c) Inductance (d) None of these

Ans : (a)Resistance

9.The SI unit of resistance is :

(a) Newton (b) Ohm (c) Watt (d) Joule Ans : (b) Ohm

17.Which of the following statement is not true, regarding the electrical set-up for the verification of Ohms law:

(a) The voltmeter is connected in parallel with the known resistance

(b) The ammeter is connected in series circuit(c) The rheostat can only increase the resistance in electric circuit

(d)The single key is used to switch on/off the electric circuit

Ans :(c) The rheostat can only increase the resistance in electric circuit

18. A voltmeter is used to find p.d. in any electrical circuit which of the statement given below is true :

(a) A voltmeter is a high resistance instrument and is connected in series circuit

(b) A voltmeter is a low resistance instrument and is connected in series circuit

(c) A voltmeter is a high resistance instrument and is connected in parallel circuit

(d)A voltmeter is a low resistance instrument and is connected in series circuit

Ans :(c) A voltmeter is a high resistance instrument and is connected in parallel circuit

19. A battery of 12V is connected in series with resisters of 0.2 ohm , 0.3 ohm,0.4 ohm,0.5 ohm and 12 ohm. How much current would flow through the 0.3 ohm resister

(a) 0.895A (b) 1.11A (c) 0.5A (d)none of these

Ans : (a) 0.895A20.Among which of the following resistance does not depend : (a) length of conductor (b) area of cross-

section (c) temperature (d)density Ans : (d)density

10.In parallel combination of electrical appliances, total electrical power

a. Increases b .Decreases c. Does not change d. Remain same.

11.The total work done by an electrical appliance during its operation, is called electrical

a. Current b. Power c. Energy d. Potential

12.The number of joules in 1kWh is a.3.6x107 b.3.6x106 c.3.6x105 d.3.6x104

13.When electric current flows through a conductor, it

a. Gains electrons b. Loose electrons

c. Becomes hot d. No change is observed.

14.Heating of a current carrying conductor is due to

a. Loss of kinetic energy by atoms

b. Loss of kinetic energy by electrons

c. Attraction between electrons

D. Repulsion between electrons ; protons

15.The correct relation between heat produced &electric current flowing

a. H I b. HI2 c. H1 /I d. H1/ I2

16.The relation between H ;I is called

a. Newton s law b. Faraday s law

c. Joules law d. Ohm s law

17.In electric heating appliances, the material of heating element is

a. Brass b. Nichrome c. Silver d. Copper.

18. Formula for electric power is

a. P= V2 I b .P=V I c .P=I/V d. P=V/I.

19.Lamps of 40 watt&60 watt are connected in parallel, the total power of combination is

a.40 watt b.60 watt c.24 watt d.100 watt

10.The resistance of a conductor is directly proportional to :

(a) its area of cross-section (b) density (c) melting point (d) length

Ans : (d) length

11.The resistance of a conductor is inversely proportional to its :

(a) area of cross-section (b) length (c) specific resistance (d) density

Ans :(a) area of cross-section

12.A current of 2A flows trough a conductor whose ends are at a p.d of 4V. The resistance of the conductor is :

(a) 8 (b) 0.5 (c) 6 (d) 2

Ans: (d) 2

13.The rheostat is used in the circuit to :

(a) increase the magnitude of current only

(b) decrease the magnitude of current only

(c) increase or decrease the magnitude of current

(d) none of these

Ans :(c) increase or decrease the magnitude of current

14.During the verification of Ohms law :

(a) ammeter and voltmeter should be connected in series

(b) ammeter should be connected in series and voltmeter in parallel

(c)ammeter should be connected in parallel and voltmeter in series

(d) ammeter and voltmeter should be connected in parallel

Ans:(b) ammeter should be connected in series and voltmeter in parallel15.Which of the following laboratory apparatus is not used during the verification of Ohms law :(a) Voltmeter (b) Ammeter (c) Galvanometer (d)Rheostat

Ans : (c) Galvanometer

See for more : (Practice) MCQ of Electricity

You might also like: Numericals On Motion test paper Solved current electricity numerical for class 10 CBSE NCERT physics Reflection and refraction MCQ solved X Human Eye and the Colourful World (MCQ)Multiple choice questions Linkwithin Posted by J Sunil at Monday, April 30, 2012 1 comments Email This BlogThis! Share to Twitter Share to Facebook Labels: 10th Electricity and Effects 28 April 2012CBSE X Current Electricity Worksheet for CBSE Exam

Chapter: Current Electricity Worksheetby Jsunil Tutorial1. Define electric current, state its unit, list the equation defining electric current.2. List three types of energy that may be used to produce current, and list three devices that provide this type of energy.3. List three types of loads and list the energy conversions taking place inside each one.4. What is the definition of voltage? What is its unit?5. Prove that 1 J is equivalent to 1 Vx A x s.6. How long does it take a current of 5.0 mA to deliver 15 C of charge?7. What is the potential difference between two points if 1.0 kJ of work is required to move 0.5 C of charge between the two points?8. What is the voltage of a source which provides 12.0 J to each Coulomb of charge present?9. What is the energy of an electron accelerated through a potential difference of 100.0 kV? (charge of an electron 1.6 x 10-19Coulomb)10. What is the potential difference between two points when a charge of 80.0 C has 4.0 x 10^3J of energy supplied to it as it moves between the two points?11. There is a current of 0.50 A through an incandescent lamp for 5.0 min, with a voltage of 115 V. How much energy does the current transfer to the lamp? What is the power rating of the lamp?12. If there is a current of 2.0 A through a hair dryer transferring 15 kJ of energy in 55 s, what is the potential difference across the dryer?13. An electric drill operates at a potential difference of 120V and draws a current of 6.0 mA. If it takes 45 s for the drill to make a hole in a piece of wood, how much energy is used by the drill?14. An electric toaster operating at a potential difference of 115 V uses 34 200 J of energy during the 20 sec it is on. What is the current through the toaster?15. A motor draws a current of 2.0 A for 20.0 sec in order to lift a small mass. If the motor does a total of 9.6 J of work calculate the voltage drop across the motor.16. In a lightning discharge, 30.0 C of charge moves through a potential difference 108 V in 20 min. Calculate the current of the lightning bolt.17. How much energy is gained by an electron accelerated through a potential difference of 3.0 x 10^2 V?18. A 12V car battery can provide 60.0 A for 1.0 h. how much energy is stored in the battery?19. How much energy is required to dry your hair if the hair dryer draws 12.0 A from a 110 V outlet for 12.0 min?Electric Circuits:1. a) Describe the difference between current in a series circuit and current in a parallel circuit.b) Describe the difference between voltage in a series circuit and voltage in a parallel circuit.2. Draw a schematic diagram of the following circuit: One power source and a resistor are connected in series with a combination of 3 light bulbs connected in parallel with each other. Include a fuse, 4 switches, a voltmeter, and an ammeter. The fuse should protect the whole circuit, one switch should shut off the whole circuit and the other switches should control the individual bulbs. The ammeter should read I and the voltmeter the voltage of the resistor.3. a) What is a short circuit?b) Why is it dangerous?c) Give two ways to protect against short circuits.4. Describe the effect on the rest of the bulbs in problem two when one burns out. Will the remainder glow brighter? dimmer? What will be the effect on the source?5. Describe resistance, list 4 factors affecting resistance.6. A conductor has a length of 2.0 m and a radius of 3.0 mm. If the resistance is R = 100 S, calculate the new resistance if the same material has:a) length = 6.0 m and r = 6.0 mmb) length = 1.0 m and r = 1.0 mm7. List two ways to increase the current drawn by a circuit.8. Draw a graph of V-I for 2 resistors and indicate which has the greatest resistance and why.9. A voltmeter measures a voltage drop of 60.0 V across a heating element while an ammeter reads the current through it as 2.0 A. What is the resistance of the heating coil?10. How much current flows through a 7.5 S lightbulb with a potential difference of 1.5 V?11. What is the voltage drop across an element which draws a current of 5.0 A and has a resistance of 40 ohms?12. A set of 6 motors is connected in series to a 120 V source drawing 1.0 A of current. Find:a) R totalb) R of each motorc) Voltage drop across each load.13. Do resistors in parallel increase or decrease total resistance?14. What resistance must be added in series to a circuit containing a 33 ohm resistor in in order to draw 2.0 A of current from a 120V source?15. How much energy is dissipated in 10 minutes when a current of 4.0 A is flowing through a potential drop of 60.0 V?You might also like:

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Linkwithin Posted by J Sunil at Saturday, April 28, 2012 1 comments Email This BlogThis! Share to Twitter Share to Facebook Labels: 10th Electricity and Effects 18 April 2012Heating Effect of Electric Current and Electrical Power CBSE PHYSICS By JSUNILHeating Effect of Electric CurrentWhen charge (electron) move through conductor ,collide with atoms of the conductors due to resistance and transfer energy to the conductor which appear as heat .Hence work done by electron to overcome resistance is equal to heat generated in conductors.Let W work done to move Q charge through a conductor of resistance R that appear as HeatW = H But , V = W/Q W = Q V H = QV But, I = Q /t Q = It\ H = V I t Also, V = IR H = It x IR H =I2Rt

Electrical Power:The rate of doing work in moving charge through conductorsOR, The rate of producing heat in conductorOr, Rate of producing electrical EnergyP = W/ tOR, P = H/t But, H =I2RtP = I2Rt /t P = I2RAlso we may express Power as P = I x I x RUsing V =IRP = VISI unit of POWERP = H/t = 1J/1Sec = WattIf 1oule energy consumed by device in 1 sec Its power said to be 1 wattCommercial electrical Energy unit is kWhWe know that P = H/t H = Pt If 1 kW (1000watt) energy consumed for 1 hour It is called 1unit(BOT unit)Energy in term of joule:H = 1kWh = 1000W x 3600sec =1000J/sec x 3600sec = 3.6 x 106 jNumerical X Current Electricity Numerical Practice worksheetRead more You might also like: X Electric Current and Its Effect CBSE -1 Most Important Questions Guess Paper SA-1- 2011 - X -Science-Electricity and its effects CBSE Physics Numerical based on chapter - Electricity & its effects For (Class X) CLASS X solved questions -Magnetic effects of electric current Linkwithin Posted by J Sunil at Wednesday, April 18, 2012 0 comments Email This BlogThis! Share to Twitter Share to Facebook Labels: 10th Electricity and Effects 15 March 2012X Electric Current and Its Effect CBSE -1 Most Important Questions 1. How do we express electric current?2. What is an electric circuit?3. What does a switch do?4. Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges. Why?5. What is the SI unit of electric charge? How many electrons make one coulomb of charge?6. Define the SI unit of current.7. Which instrument is used to measure the current flowing in a circuit? How is it connected in the circuit and why?8. In which smaller units can we measure the small amount of current flowing in the circuit?9. How are the related to the SI unit of current?10. What makes the electric charge to flow?11. State the energy conversion taking place in (a) Electric cell (b) Electric torch12. Define the electric potential difference between two points in an electric circuit carrying some current.13. Define the SI unit of Electric potential.14. Which instrument is used to measure the electric potential difference between two points in a circuit? How is it connected in the circuit and why?15. State the law relating the potential difference across a conductor and the current through it?16. The VI graph is a straight line that passes through the origin of the graph. What do you conclude from this observation?17. Define resistance of a material. Define its SI unit.18. Which component is used to regulate current without changing the voltage source in an electric circuit?19. Fill in the blanks(a) A component of a given size that offers a low resistance is a ________________. (b) A conductor having some appreciable resistance is called a ______________. (c) A component of identical size that offers a higher resistance is a ____.. (d) An _____________ of the same size offers even higher resistance.20. Define the commercial unit of energy. Relate it to joules.21. Discuss the activity to show that resistance of a conductor depends on its length and area of cross section.22. What is the electrical resistivity of the material of the conductor? What is its SI unit?23. Which common factor affects both resistance as well as resistivity and how?24. Alloys are commonly used in electrical heating devices. Why?25. When a number of resistors are connected in series in a circuit what would be their equivalent resistance and why?26. When a number of resistors are connected in parallel in a circuit what would be their equivalent resistance and why?27. It is impracticable to connect an electric bulb and an electric heater in series. Why?28. What is heating effect of electric current. Name the various devices in which this effect is utilized.29. State the Joules law of heating. Derive the expression for the same.30. Which effect of current is responsible for the glow of an electric bulb? Explain.31. The bulbs are usually filled with few gases. Name those gases. Also discuss the cause for the same.32. Which metal is used as the filament of an electric bulb and why?33. How does a fuse work in the electric circuit?34. Which materials are preferred for a fuse wire and why?35. Give the ratings of various fuses used in the domestic circuit.36. Why is Tungsten metal selected for making filaments of incandescent lamp bulbs?37. A torch bulb is rated at 3V and 600mA. Calculate its a) Powerb) Resistance c) Energy consumed if it is lighted for 4 Hrs.38. Which will offer more resistance a 50W lamp or 25W lamp bulb and how many times?39. Why should the heating element of an electric iron be made of iron, silver or Nicrome wire?40. If a wire is stretched to triple its original length, what happens to its resistively?41. Two identical resistors each of resistance 10 ohm are connected 1) in series 2) in parallel, in line to a battery of 6volts. Calculate the ratio of power consumed in the combination of resistors in the two cases.42. A bulb is rated at 220V- 100W. What is its resistance? Five such bulbs burn for 4 hrs. What is the energy consumed? Calculate the cost if the rate is 50paise per unit?43. Two lamps rated 100W, 220V and 25W, 220V are connected in parallel to 220V supply. Calculate the total current through the circuit.44. A metallic coil connected to a 220V supply has a resistance of 110 ohm. How long will it take this coil to heat 1kg water from 2o0C to 700C? Assume whole heat produced by coil is taken up by water. (Specific heat capacity of water = 4186 )45. Why is much less heat generated in long electric than in filaments of electric bulb?46. How does the resistance of wire change when 1) Its length is doubled 2) Area is doubled?47. An electric kettle rated 1000W, 220V is used to bring water at 20 degrees to its boiling point. If the kettle is switched on for 10 minutes. Calculate: a. The resistance of the element of kettleb. Current flowing through the element c. Mass of water in the kettle.48. A copper wire has a diameter of 0.5mm and resistively of . How much of this wire is required to make a 10 ohm coil?49.A wire of resistance 5ohm is bent in the form of a closed circle. What is the effective resistance between the two points at the end of any diameter of the circle?50. What is the effect on resistively of a pure metal with the increase in temperature?