D A V PUBLIC SCHOOL HEHAL RANCHI

CLASS-XII SUBJECT-BIOLOGY

1. Meiosis takes place in –

a) Megaspore b) Meiocyte c) Conidia d) Gemmule

2. In water hyacinth vegetative propagation occurs by –

a) Offset b) Rhizome c)Leaf bud d)Bulbil

3. Flowers are unisexual in –

a) Pea b) Cucumber c) China rose d) Onion

4. Formation of embryo directly from nucellus and integument is –

a) Adventitivepolyembryony b) Apospory c) Apogamy d) Apomixis

5. Development of seed from an unfertilized egg is –

a) Vivipary b) Parthenocarpy c) Apogamy d) Apospory

6. Night blooming flowers are generally –

a) lightweight b) white c) brightly coloured d) bloom in clusters

7. Which one is triploid?

a) Megaspore b) Embryo c) Endosperm d) Microspore

8. Scutellum is a part of –

a) Dicot embryo b) Monocot embryo c) Pistil d) Leaf bird

9. Filiform apparatusis characteristic feature of–

a) Generative cell b) Nucellar embryo c) Aleurone cell d) Synergids

10. Persistent nucellus in the seed is called–

a) Chalaza b) Perisperm c) Hilum d) Tegmen

11. In an embryo sac, the cells that degenerates after fertilization are–

a) Synergids& Pr. Endosperm cell c) Antipodal cells & Pr. Endosperm cells

b) Synergids& Antipodal cells d) Egg & Antipodal cells

12. Oogenesis occurs in –

a) Squamous epithelium of ovary b) Interstitial cells of ovary c) Follicals of

ovary d) Germinal epithelium of ovary

13. Signals for parturition originate from–

a) Placenta b) Fully developed foetus c) Both (a) & (b) d) Oxytocin

14. Sertoli cells are controlled by the pituitary hormone –

a) FSH b) GH c) PRL d) LH

15. Leydig cells secrete –

a) Progesterone b) Testosterone c) Estrogen d) Cortisol

16. In uterus endometrium increases in thickness in response to–

a) Oxytocin b) Estrogen c) LH d) Relaxin

17. Spermatids are changed into sperm through –

a) Spermiogenesis b) Spermiation c) Spermatogenesis d) Spermatosis

18. Hormone controlling human menstrual cycle is –

a) Estrogen b) FSH c) LH d) All the above

19. Antrum is a cavity of –

a) Ovary b) Graafian follicle c) Blastula d) Gastrula

20. Notochord skeletal system & dermis of skin are derived from –

a) Ectoderm b) Endoderm c) Mesoderm d) All the above

21. Which of the following is a hormone releasing intrauterine device –

a) LNG-20 b) Cervical Cap c) Vault d) Multiload 375

22. Lactational amenorrhoea prevents –

a) Milk secretion b) Conception c) PRL secretion d) Spermatogenesis

23. Which one is a method of birth control?

a) IVF-ET b) HTF c) GIFT d) IUD

24. Test tube baby program uses one of the following techniques–

a) Intrauterine insemination b) Intracytoplasmic sperm injection c) Gamete

intrafallopian transfer d) Zygote intrafallopian transfer

25. Cu-T prevents

b) Ovulation b) Implantation c) Sperm entry d) Fertilization

DAV PUBLIC SCHOOL, HEHAL, RANCHI-05 TOPIC-SOLUTIONS Set: 1

1 Define molality.

2 What is meant by 10% (m/m) aqueous solution of NaCl.

3 Define molarity.

4 Define the term mole fraction .

5 Explain how molarity value of a solution can be converted into its molality.

6 What do you mean by M/10 HCl solution ?

7 What is the relationship between molality and mole fraction of solute in a solution ?

8 What is the effect of temperature on the solubility of solids in liquids ?

9 State Henry’s law.

10 State Raoult’s for the solution containing volatile liquids.

11 State Henry’s Law.Write its one application. What is the effect of temperature on solubility of gases in liquids.

12 State Raoult’s for a solution containing non volatile solute. What type of deviation from Raoult’s is shown by a solution of chloroform and acetone and why ?

13 (i)Why are aquatic species more comfortable in cold water than in warm water ? (ii)What happens when we place the red blood cells in saline water (hypertonic solution) .Give reason.

14 What are ideal and non ideal solution solutions? Give reason for the formation such solutions. Write four differences between ideal and non ideal solution.

15 Write differences between solution showing positive and negative deviation from raoult’s law.Also plot graph for positive and negative deviation.

16 Why sodium chloride solution boil at higher temperature than water but freezes at lower temperature than water ?

17 What are colligative properties ? How is the colligative properties of solution changed when a solute in a solution undergoes (i) association (ii) dissociation.

18 Define osmotic pressure.How is it that measurement of osmotic pressure is more widely used for determining molar masses of macromolecules than the rise in boiling point or fall in freezing point of their solutions ?

19 The depression in freezing point of water observed for the same amount of

acetic acid, trichloroacetic acid and trifluroacetic acid increase in the order as stated above .Explain briefly.

20 Calculate the mass of compound (molar mass =256 ������ ) to be dissolved in 75 g of benzene to lower its freezing point by 0.48 K (� = 5.12

� �� ����� ) 21 Find the molarity and molality of a 15%(mass/mass) solution of H2SO4

(density =1.02 � ���� ) 22 Calculate the boiling point of a solution when 2 g of Na2SO4 was dissolved in

50 g of water , assuming that it undergoes complete ionozation. 23 If N2 gas is bubbled through water at 298 K , how many moles of N2 gas

would dissolve in 1 litre of water ? Assume that N2 exerts a partial pressure of 0.987 bar. Given that Henry,s law constant for N2 at 298 K is 76.48 k bar .

24 Benzoic acid completely dimerises in benzene. If the vapour pressure of pure benzene at the temperature of experiment is 66.6 torr , then what will be vapour pressure of a solution containing 61 g of benzoic acid per 500 g of benzene ?

25 A 5% solution of cane sugar (molar mass =342 � ����� ) is isotonic with 0.877% solution of urea . Calculate the molar mass of urea.

***

DAV PUBLIC SCHOOL, HEHAL, RANCHI-05

TOPIC-SOLUTIONS

Set: 2

1 State Raoult’s law for a solution containing a non –volatile solute

and volatile solvent. 2 What are azeotropes ?

3 Why do gases always tend to be less soluble in liquids as the temperature is raised ?

4 Define molal elevation constant or ebullioscopic constant.

5 Define molal depression constant or cryoscopic constant.

6 Which of the following has higher boiling point and why ? 0.1 M NaCl or 0.1 M glucose .

7 Define Osmotic pressure.

8 Explain the term reverse osmosis. What is the large scale use of it.

9 Define Vant’ Hoff Factor (VHF).

10 What is the VHF for following compound which undergoes (i)CaCl2 (50% dissociation) (ii)K4[Fe(CN)6] (100%dissociation)

11 15 g of an unknown molecular substance was was dissolved in 450 g of water , the resulting solution freezes at – 0.34 ℃. What is the molar mass of the substance ? ((� = 1.86 � �� �����)

12 Calculate the freezing point depression expected for 0.0711 m aqueous solution of sodium sulphate. If the solution actually freezes at – 0.320 ℃ , What is the actual value of vant’s Hoff factor at this

temperature ?( (� = 5.12 � �� �����)

13 A 1.00 molal aqueous solution of trichloroacetic acid (CCl3COOH) is heated to its boiling point.The solution has the boiling point of 100.18 ℃ . Determine the vant’s Hoff factor for trichloroacetic acid.(�� for water is 0.512 � ������� )

14 Determine the osmotic pressure of a solution prepared by dissolving 2.5 × 10�� g of K2SO4 in 2 litre of water 25℃ assuming that it is completely dissociated. ( R =0.0821� ��� �������� )

15

2 g of benzoic acid dissolved in 25 g of benzene shows a depression in freezing point equal to 1.62 K .Molal depression constant (Kf of benzene is 4.9 � �� �����) What is the percentage association of the acid if it forms dimer in the solution ?

16 KI and sucrose solution with 0.1M concentration have osmotic pressure of 0.465 atm and 0.245 atm respectively. Find the vant’s Hoff’s factor of KI and its degree of dissociation.

17 Calculate (a) molality (b) molarity (c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.2 � ����.

18 The vapour pressure of pure liquid A and B are 450 and 700 mm Hg respectively at 350 K. Find out the composition of the liquid mixture if the total vapour pressure is 600 mm Hg.Also find the composition of the vapour phase also.

19 Henry’s law constant for CO2 in water is 1.67 × 10� Pa at 298 K. Calculate the quantity of CO2 in 500mL of soda water when packed under 2.5 atm CO2 pressure at 298 K.

20 H2S, toxic gas with rotten egg like smell, is used for qualitative analysis .If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.

21 Discuss biological and industrial application of osmosis.

22 A decimolar solution of potassium ferrocyanide is 50% dissociated at 300 K .Calculate the osmotic pressure of the solution. {decimolar solution means molarity is 1/10 } { Potassium ferrocyanide = K4[Fe(CN)6 }

23 Suggest the most important type of intermolecular interaction in the following pairs: (i) n-hexane and n- octane (ii) I2 and CCl4 (iii) NaClO4 and water (iv) methanol and acetone (v)acetonitrile(CH3CN) and acetone (CH3COCH3)

24 Among the following compounds identify which are insoluble, partially soluble and highly soluble in water (i) Phenol (ii) tolune (iii) formic acid (iv) ethylene glycol (v)Chloroform .

25 Calculate the mass of non-volatile solute (molar mass 40 g/mol) which should be dissolved in 114 g of octane to reduce its vapour pressure to 80% .

***

ASSIGNMENT-1 Subject: English Class: XII WRITING SECTION (CLASSIFIED ADVERTISEMENT)

1. You are Mohan/Mohini, General Manager of PK Industries, Hyderabad. You need an accountant for your company. Draft an advertisement for the classified columns of ‘The Hindustan Times’ in not more than 50 words.

2. You are Ratan/Ram, General Manager of Hotel Green Park,Ranchi. You need a receptionist for your hotel. Draft an advertisement in not more than 50 words to be published in ‘The Telegraph’, Ranchi, calling for applicants.

3. Samta Public School, Delhi requires cricket and hockey coaches. Draft a suitable advertisement in about 50 words for the ‘Situation Vacant’ column of ‘The Daily Herald’, stating the requirements regarding age, qualification, experience, etc. You are the Principal of the school.

4. You are Krishna/Tisha, Secretary, Greenland Enterprises, Ltd., Delhi-6. Your chairman has asked you to draft an advertisement for a local daily under the classified columns for the vacant posts of one accountant and two office assistants. Draft an advertisement in not more than 50 words.

5. You are the General Manager of Ivry Software Solutions, Agra Cantt., Agra. You need a software engineer in your organisation. Draft an advertisement in not more than 50 words to be published in ‘The Times of India’ under classified columns. NOTICE WRITING

1. You are Sanjay/Sangeeta. As President of the Excursion Club you have organised an excursion to Kathmandu (Nepal) during the summer vacation for the senior students of your school. Write a notice in about 50 words informing the students about the proposed excursion.

2. You are Abhinav/Abha. You have planned a two week course to be arranged to help the children of your Group Housing Society at Bokaro, acquire the oral communication skills. Prepare a notice for the Society’s Notice Board, stating the objectives of the course, giving necessary details and requesting the children of the society to join it.

3. Your school, Adarsh Vidyalaya, Ranchi, is organizing a lecture by the famous writer Vikram Seth on the occasion ‘Literacy Week’ being celebrated in your school. Write a notice informing your students about the lecture. Invent necessary details.

4. On account of the solar eclipse on 11th August 2020, your Principal decides to declare a holiday. But in lieu of it, Saturday will be a full working day. As the Head Boy, draft a notice informing the students about the same.

5. You are Rahul/Rashmi. As President of the Literary Club of your school, you have organised an Inter-School Debate Competition on the occasion of Silver Jubilee Celebrations of your school. Write a notice in not more than 50 words, informing the students of your school about the competition. FORMAL LETTERS

1. You are Varsha/Varun, In charge of Excursion Club of BVP School, Mathura Road, Delhi. Write a letter to the General Manager, Northern Railways, requesting reservation of a bogie for 80 students from New Delhi to Chennai and back by GT Express.

2. Write a letter to the Municipal Chairman of New Town, North Arcot District about the dilapidated condition of the public monument requesting him to take urgent steps for the preservation of this valuable heritage. You are Karan/Karuna, 10 Pudupet, New Town.

3. You are Rama/Ram, residing at 75A Nehru Nagar, Meerut. An open and well maintained park meant for the residents and children of your area will soon be converted into a shopping complex. Write a letter to the Commissioner of the Municipal Corporation, Meerut requesting him not to disturb the park which is the only open space in your area. Also suggest alternative space for the shopping complex away from the residential area, giving suitable reasons.

4. Due to insanitary conditions in the colony, the population of rodents has been multiplying exposing the residents to multiple diseases. Write a letter to the Municipal Commissioner bringing the problem to his notice and urging him to take urgent action in the matter. You are Suraj/Supriya, 12 MG Road, Chennai.

5. The drinking water supplied to your locality Anandlok Colony, Ranchi has a dirty colour and a foul smell. As secretary of the Residents Welfare Association, write a letter in 120-150 words to the Chief Engineer, Water Authority, Ranchi complaining about the problem and requesting him to take necessary action at the earliest.

ARTICLE WRITING

1. Today’s youth are very fashion conscious. Write an article in about 150-200 words for your school magazine, describing · Modern youth’s craze for fashion · Different areas of fashion-clothes, accessories, gadgets, etc

· Reasons why fashion changes very fast · Problems being fashionable may cause

2. More and more parents are working these days and children have more and more access to the internet. Unrestricted and unmonitored access to the internet puts children at a lot of risk of being bullied, blackmailed and exploited. Write an article for a newspaper highlighting the problem. In your article you should · describe the problem of unrestricted internet access by children · say how children are at risk · suggest some ways of ensuring children safety while they are online

3. Communal hatred and violence have time and again threatened to disintegrate our country. But India is known for assimilation of new religions, cultures and communities. The onus of uniting and integrating the country despite its diversity is now on the shoulders of its youth. Write an article for a newspaper on the topic: ‘Role of Youth in Communal Harmony’.

4. Pizzas, burgers, noodles, French fries, potato chips fall under the category of hazardous fast food which along with soft drinks, result in health hazards like malnutrition, obesity, hypertension, higher amounts of bad cholesterol, risk of heart attack, and diabetes. It is not an occasional intake but the binge of fast food that is harmful. Write an article on the harmful effects of fast food and the need of introducing healthy and nutritious food in daily diet.

5. India is a young and vibrant democracy that needs to mature and consolidate its position in the world. The only people who can make that happen are the young voters-people in the age group of 18-30. Write an article in about 150-200 words advising these people how to exercise their right to vote. In your article you should say · why it is important for everyone to vote · what different factors young voters should consider before they vote-parties,

policies, candidates, issues · how one can register himself/herself as a voter

ASSIGNMENT-2 Subject: English Class: XII WRITING SECTION REPORT WRITING

1. You have witnessed a clash between a group of college students and the State Transport bus crew, which finally ended up in stoning the buses and the bus crew calling for a clash strike. You are Santosh/Seema, a reporter for “The Hindustan Times”. Write a report in about 100-125 words about the incident.

2. Write a report in about 125 on a One Day Cricket Match played by your school (i.e. Kamla Nehru Vidyalaya) against A.C.Ganguly Senior Secondary School, Amethi.

3. You are Umesh/Usha. As the President of a voluntary organization you have visited a slum area in your city destroyed in a massive fire. Write a report on the tragic situation of these homeless people to be published in a magazine.

4. You are Sunderi/Savi of Rajeev Gandhi Memorial Sr. Secondary School, Allahabad. Your school has just inaugurated its new Computer Wing, constructed with generous grants from the Rajeev Gandhi Foundation. Write a report in not more than 125 words for your school magazine, on the programme organized by your school on this occasion.

5. As a Staff Reporter of “The Times of India”, who witnessed a multiple collision of a Maruti car, a scooter and a Tourist bus in a road accident, write a report in not more than 100-125 words for the publication in the newspaper.

6. Write a report in about 125 words on “No Tobacco Day” programme organized by your school on 4th June 2020.

7. Your school has recently celebrated its Silver Jubilee, organising a number of inter-school competitions and awarded prizes in a gala function. As the Secretary of the Cultural Club of your school, write a report in 125 words for your school magazine. ARTICLE AND SPEECH WRITING

1. You are Ram/Rajani. Write a speech on “Importance of Morning Walk”. 2. As Principal of your school you have found some students reaching the school late

in the morning, coming late to their classrooms after recess and returning lazily to the theory class after doing practicals in the laboratory. Write a speech in about 150-200 words that you will deliver on the importance on discipline and punctuality in life.

3. Sakshi Malik won a bronze medal in the Rio Olympics. Every Indian felt proud of her. You, Head Girl of your school want to deliver a speech in order to express your feelings. Write the speech in 150-200 words. Apart from your ideas use the following clues: Wrestling only a male sport-Sakshi born in conservative surroundings-most unfavourable gender ratio for females-parental encouragement-one can’t forget the look of determination on her face in the last three minutes of the bout.

4. After the rainy season is over, mosquitoes start breeding. They cause malaria, dengue, chikungunya, etc. These diseases can sometimes prove fatal. As Principal of your school, you have decided to deliver a speech on protection from mosquitoes. Write that speech in 150-200 words.

5. The students of your school got 100 percent marks in various subjects in Senior School Certificate Examination this year. The achievement was made through the efforts made by the students under the guidance of their teachers. Write a speech congratulating the teachers and the students.

6. You are Suraj/Sunita. Write an article in 150-200 words, on the topic “Rapid increase in the number of private cars and its effects on Environment”.

7. You are Anita/Rajan. You are concerned about the growing problems of obesity in children which leads to Type-II diabetes. Write an article in 150-200 words titled “Health-the Best Wealth” throwing light on what problems arise if we eat junk food or overeat and neglect our health, and how we can maintain good health through right food and good habits. FORMAL LETTERS

1. You are Ankit/Amrita, staying at 4, Pycrofts Road, Chennai. You have come across an advertisement in “The Times of India” for recruitment of Computer Engineer Trainees by Shivam Software. Aplly in response to this advertisement, giving your detailed bio data (curriculum vitae).

2. You are Anand/Arti, Model Town, Delhi. You have seen an advertisement in “The Hindu” for the post of Chief Chef in a 5-Star Hotel. Apply for the job with complete bio data.

3. You are Ketan Pandey of 63, Civil Lines, Delhi. You saw an advertisement in “The Hindu”for the post of accountant in a reputed firm. Write an application in about 120-150 words to the area manager of Gayatri Consultants, 2, Station Road, New Delhi, giving your detailed bio data.

4. You are Prem/Parul of 16 TT Nagar, Bhopal. You would like to apply for the post of Marketing Manager in a reputed firm in Mumbai. Write a letter in about 120-150

words to the Public Relations Officer, Chantac Enterprises, Mumbai applying for the job.

5. You are Rahul/Rishi, a student of class XII. Recently, a group of 20 students including you went to Chhatbir Zoo for two days. You were shocked to see the poor arrangements made by Messrs Adventure Tours and Travels who had taken the responsibility of that tour. Write a letter to the Manager complaining about the mismanagement.

6. Mr. Satish Kaul is the sports instructor in Geeta Convent, Naraspur. The Principal of the school asks Mr. Kaul to place an order for buying cricket kits, volleyball nets, footballs, badmintons and the necessary sports accessories required. Mr. Kaul decides to place an order with Messrs Lohia Sports Equipment, Naraspur. Write the order letter in about 150-200 words.

7. Write a letter to the Manager, Bata Shoe Company, Faridabad complaining about the quality of shoes bought by you from their local showroom. Mention the cash memo and the design number.

8. You are Anshuman/Rashi staying at 8, Kakatya Nagar, New Delhi. Last month, you bought a video camera from the ‘Ultra Modern Electronic House’, Abids, Hyderabad against a warranty of two years. Now you discover that there is something wrong with this camera. It doesn’t work for more than 30-40 seconds at a stretch and its zoom gets stuck now and then. Write a letter to the dealer complaining about this problem. Also request him to replace this defective piece against the warranty period.

DAV PUBLIC SCHOOL, HEHAL, RANCHI-05

PHYSICS ASSIGNMENT-1

TOPIC: ELECTROSTATICS/ CHARGE AND PROPERTIES OF CHARGES

1. In a neutral sphere 5 x 1021 electrons are present. If 10 percent electrons are removed, then

calculate charge on sphere. [Ans: 80 C]

2. Calculate number of electrons in 100 gram of CO2. [Ans: 3 x 1025 electron]

3. Can a body have a charge (a) 0.32 x 10-18 C (b) 0.64 x 10-20 C (c) 4.8 x 10-21 C.

[(a) Yes, (b) No, (c) No]

4. A glass contains 1 billion Amoeba and two sodium ions are deposited on body of every Amoeba.

Find out the charge contained glass.[Ans: 3.2 x 10-10 C]

5. How many electrons should be removed from a conductor so that it acquires a positive charge of

3.5 nC? [Ans: 2.18 x 1010 C]

6. A) Explain the meaning of statement ‘electric charge of a body is quantised’.

B) Why can one ignore quantization of electric charge when dealing with macroscopic i.e., large

scale charges?

7. Is quantization of charge valid, after the presence of quark particles. Explain it.

8. It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are

themselves built out of more elementary units called quarks. A proton and a neutron consist of

three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge + (2/3)

e, and the ‘down’ quark (denoted by d) of charge (–1/3) e, together with electrons build up

ordinary matter. (Quarks of other types have also been found which give rise to different unusual

varieties of matter.) Suggest a possible quark composition of a proton and neutron..

9. A polythene piece rubbed with wool is found to have a negative charge of 3.2 x 10-7 C. Calculate

I. the number of electrons transferred. [Ans: 2 x 1012 electrons]

II. mass gained by the polythene. [Ans: 18.2 x 10-19 kg]

10. Two identical metal spheres A and B are supported on insulating stand and placed in contact. What

kind of charges will A and B develop when a negatively charged ebonite rod is brought near A.

[Ans: A: positive, B: negative]

11. What does q1 +q2 = 0 signify in electrostatics?

12. A soap bubble is given a negative charge, then how its radius will change? [Ans: will increase

first then becomes constant]

13. A glass rod rubbed with silk is brought close to two uncharged spheres in contact with each other

inducing charges on them as shown in figure. Explain with diagram in each case, what happens

when

I. The spheres are slightly separated?

II. The glass rod is subsequently removed?

III. The spheres are separated far apart?

DAV PUBLIC SCHOOL, HEHAL, RANCHI-05

PHYSICS ASSIGNMENT-2

TOPIC: ELECTROSTATICS/ COULOMB’S LAW

1. If dielectric constant of water is 81, then what is its permittivity? [Ans: 810

ε ]

2. The dielectric constant of medium is unity, then what will be its permittivity? [Ans: 0

ε ]

3. Force between two point electric charges kept at a distance d apart in air is F. If these charges are kept at the

same distance in water, how does the force between them changes? [Ans: /water airF F k= ]

4. How does the force between the two point charges change if the dielectric constant of the medium in which

they are kept increases? [Ans: force decreases]

5. A force F is acting between two charges placed some distance apart in vacuum. If brass rod is placed between these two charges, how does the force change? [Ans: 0]

6. If the distance between two equal point charges is doubled and the magnitude of each charge is also doubled

then what would happen to force between them? [Ans: remain same] 7. How does the coulomb force between two point charges depend upon the dielectric constant of the intervening

medium? [Ans: 1/F k∝ ]

8. Define dielectric constant of medium in terms of force between electric charges?

9. The electrostatic force between two charges is a central force. Why?

10. Two point charges q1 and q2 are placed close to each other in air. What is the nature of force between then when (i) q1q2 > 0 (ii) q1q2 < 0

11. Force of attraction between two point charges placed at distance d in air is F. What distance apart should

these be kept in the same medium, so the force between them becomes (i) 3F (ii) 9F [(i) / 3d (ii) d/3]

12. Two point charges placed at a distance r in air exerts a force F on each other. At what distance will these

charges experience the same force F in a medium of dielectric constant k? [Ans: r

k]

13. Two point charges q1 and q2 at a separation r in vacuum exert a force F on each other. What should be their

separation in an oil of a relative permittivity 16, so that the force between them remains F only? [Ans: r/4]

14. Two extremely small charged copper sphere have their centers separated by a distance of 30 cm in vacuum.

(a) What is the mutual force of electrostatic repulsion if charge on each is 6 x 10-7 C? [Ans:3.6 x 10-2 N] (b) What will be the force between them

(i) If they are immersed in water of dielectric constant 80 [Ans: 4.5 x 10-4 N]

(ii) If charge on each sphere is doubled and distance between them is halved. [Ans: 2.88 x 10-1 N]

(iii) If an identical uncharged sphere C is brought in contact with the two spheres one by one and

finally removed. [Ans: 1.35 x 10-2 N]

15. Two small spheres each having a charge q are suspended by insulating threads of length l from a hook. This arrangement is taken in space, where there is no gravitational effect. Then what will be the angle between

the suspensions and the tension in each thread? [Ans: 0

180θ = (in absence of g),

2

24

kq

l]

16. Two small spheres each having mass m kg and charge q Coulomb are suspended from a point by insulating

threads each ‘ l ’ metre long, but of negligible mass. If θ is the angle, each string makes with the vertical

when equilibrium has been attained, show that 2 2 2

0(4 sin . tan )4q mgl θ θ πε=

17. Two small spheres each having mass m kg and charge q Coulomb are suspended from a point by insulating

threads each ‘ l ’ metre long . Prove that equilibrium separation 1/3

2

02

q lx

mgπ

=

∈

when each thread makes a small angle θ with the vertical.

18. The force on an electron kept in an electric field in a particular direction is F. What will be the magnitude and

direction of the force experienced by a proton kept at the same point in the field? Mass of proton is about 1836 times the mass of the electron.

19. State the limitations of Coulomb’s law in electrostatics.

20. Plot a graph showing the variation of coulomb force (F) versus (1/r2), where r is the distance between the two

charges of each pair of charges: (1 Cµ , 2 Cµ ) and (2 Cµ , -3 Cµ ). Interpret the graphs obtained.

21. The sum of two point charges is 7 Cµ . They repel each other with a force of 1 N when kept 30 cm apart in

free space. Calculate the value of each charge. [Ans: 5 Cµ , 2 Cµ ]

NOW TRY:

NCERT TEXTUAL QUESTIONS : 1.1, 1.2, 1.3, 1.5, 1.6, 1.11, 1.12, 1.13, 1.31

NCERT EXEMPLAR QUESTIONS : 1.1, 1.20, 1.21, 1.23, 1.29, 1.30