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Electricity As
Date:
Time: Total marks available: Total marks achieved: ______
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QuestionsQ1.A student investigates how the efficiency of an electric motor being used to raise a load varies with the weight of the load. The time taken for the motor to lift a load from the floor to the maximum height was measured using a stopwatch. The load was varied by adding weights, each marked '1.00 N'.
The spreadsheet shows the student's results (columns A to E) and calculation (column F).
Explain how the value in cell F4 has been determined using the results obtained. (3)
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...................................................................................................................................................................... Q2.The graph shows how the current through a filament bulb varies with the potential difference across the bulb.
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(a) Determine the resistance of the filament bulb when the potential difference is 7.0 V.
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(b)Sketch a graph of resistance against potential difference for the filament bulb over the range 0 V to 7 V.
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* (c) Explain the variation of resistance with potential difference for the filament bulb in terms of particle
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behaviour.
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(Total for question = 11 marks) Q3.The photographs show two types of caliper being used, in turn, to measure the diameter of an iron rod.
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The value obtained from caliper 2 was used to determine the cross-sectional area of the rod and the electrical properties of the rod were investigated.
Calculate the drift velocity for the charge carriers in the rod when the current in the rod is 1.9 A.
diameter of rod = 12.2 mm charge carrier density for iron = 1.7 × 1029 m–3
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(Total for question = 3 marks) Q4.When food is cooked in a microwave oven, microwave radiation is absorbed by water molecules, increasing the internal energy of the food.
A student heats water in a microwave oven for 1 minute to determine the efficiency of the oven at transferring energy to the water. The current in the microwave oven is 5.0 A and the potential difference is 230 V. The increase in internal energy of the water is 29 000 J.
Calculate the efficiency of the microwave oven at heating the water.
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Q5.The diagram shows a combination of three identical resistors.
What is the combined resistance between P and Q?
A 4 Ω
B 6 Ω
C 8 Ω
D 12 Ω
Q6.When a semiconductor has its temperature increased from room temperature, its resistance usually decreases because
A the electrons are moving faster.
B the lattice atoms vibrate with greater amplitude.
C the lattice atoms vibrate with smaller amplitude.
D the number of charge carriers per unit volume increases.
Q7.The diagram shows a potential divider circuit that contains a negative temperature coefficient thermistor.
The temperature of the room containing the circuit increases.
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Select the row of the table that correctly shows the changes in readings on the meters.
Q8.A hair dryer is used for 3 minutes. The operating current is 6 A.
What charge flows in this time?
(1). A 0.03 C
B 2 C
C 18 C
D 1080 C
(Total for question = 1 mark) Q9.A light dependent resistor and a negative temperature coefficient thermistor are connected in series.
Which of the following combinations of illumination and temperature will result in the highest combined resistance?
(1)
A dark and cold
B dark and hot
C light and cold
D light and hot
(Total for question = 1 mark)Q10.A student is deriving an equation for the total resistance of resistors in series.
She writes the following steps but does not justify them.
Which step is justified using conservation of charge?~ 7 ~
(1)
A Step 1
B Step 2
C Step 3
D Step 4
(Total for question = 1 mark)Q11.The current in a filament lamp is 250 mA.
How much charge flows through the lamp in 3 minutes?
A 0.75 C
B 45 C
C 750 C
D 45 000 C
(Total for question = 1 mark)Q12.A cell may be represented as an e.m.f. ε in series with an internal resistance r.
A student used the relationship V = ε − Ir and a graphical method to determine ε and r. She connected a cell in a circuit and took a series of measurements of the current I in the cell and the potential difference V across the terminals of the cell.
(a) Complete a circuit diagram of a circuit she could have used.
(2)
(b) The student's measurements are shown in the table and plotted on the graph.
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Determine values for ε and r from the graph and show how you obtained your answers.(4)
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(c) Explain how the graph could be constructed to obtain better values for ε and r.
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Q13.(a) State what is meant by drift velocity when applied to a metal conductor.
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(b) Two conductors of the same material and length carry the same current. Conductor X has twice the cross-sectional area of conductor Y.
(i)By referring to an appropriate equation, compare the drift velocities for conductor X and conductor Y.(2)
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*(ii) Explain the difference in resistance of conductor X and conductor Y in terms of the difference in drift velocity.
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(Total for question = 6 marks)
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Q14.The diagram shows the current in part of an electrical circuit.
State the relationship between I1, I2 and I3 and explain it in terms of charge.
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(Total for question = 3 marks)Q15.The diagram shows a circuit which may be used to find the emf ε and internal resistance r of a cell.
(a) As the resistance R of the variable resistor is varied, values of the current I in the circuit and the terminal potential difference V across the cell are recorded.
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Sketch the graph of V against I and explain how it may be used to determine ε and r. (5)
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*(b) We usually assume that ammeters have negligible resistance and voltmeters have infinite resistance.The determination of ε and r is not affected by using an ammeter with non-negligible resistance but is affected by using a voltmeter with a low resistance.Explain why.
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............................................................................................................................................. (Total for Question = 9 marks)Q16.A torch uses a 1.5 V dry cell. Over time, the light intensity produced by the torch decreases as the cell 'goes flat'.
Student B correctly determined the e.m.f. of an unused cell as 1.63 V and its internal resistance as 1.15 Ω.
He repeated this after the cell had been used for several weeks. When a voltmeter was connected directly across the used cell, the reading was 1.36 V. A bulb of resistance 5.92 Ω was then connected across the used cell and the reading fell to 0.84 V.
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Student A suggests that the cell goes flat as it is used because the e.m.f. decreases. Student B suggests it is because the internal resistance increases.
Determine whether either student is correct about the changes in the cell as it goes flat.
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(Total for question = 5 marks) Q17.The diagram shows a resistor of resistance R across a cell of e.m.f. ε and internal resistance r.
Which of the following is a correct expression for the current I?
A I = ε / r
B I = ε / R
C I = ε / (R + r)
D I = ε / (R − r)
(Total for question = 1 mark)Q18.When a cell of e.m.f. 1.5 V is connected across a resistance of 6.6 Ω the current is Ω.21 A.
Calculate the internal resistance of the cell.
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............................................................................................................................................. (Total for Question = 3 marks)Q19.An electric motor with potential difference V and current I lifts a mass m through a height h in time t at a steady speed v.
The efficiency of the motor is given by
(Total for Question = 1 mark)
Q20.A motor lifts a block of mass 0.050kg at a constant velocity of 0.40 m s–1.
The current in the motor is 85mA and the potential difference across it is 3.0V.
Calculate the efficiency of the motor.
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(Total for question = 3 marks) Q21.Dentists often use a white composite material for fillings for teeth. This material is applied as a liquid and then hardened using blue light.
The photograph shows a light gun, used by dentists, that emits the blue light.
(a) The light gun emits light of radiation flux 8000 W m−2.
A particular tooth needs a filling of cross-sectional area 1.5 × 10−5 m2. It requires 2.3 J of incident light energy to harden the filling.
Calculate the time for which the light must be applied.
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(b) The light gun is supplied with a rechargeable battery of capacity 1.4 amp hours. When in use, the output potential difference of the battery is 3.7 V.
(i) Assuming the potential difference is constant, show that the maximum energy supplied by the battery is about 20 000 J.
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(ii) Assuming each filling requires 2.3 J of incident light energy, a fully charged battery can be used to power the light gun to harden 210 fillings.
Calculate the efficiency of the light gun at supplying the energy stored in the battery to the fillings.(3)
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(Total for question = 8 marks)Q22.Which of the following correctly defines electromotive force?
(1) A Force per unit charge to move a charge across a component. B Force per unit charge to move a charge around a circuit. C Work done per unit charge to move a charge across a component. D Work done per unit charge to move a charge around a circuit.
(Total for question = 1 mark)
Q23.A mobile phone is powered by a lithium-ion battery. The information shown is taken from the battery.
(i) The watt-hour (W h) is an alternative unit for energy.
Show that the maximum energy that can be stored by the battery is about 25kJ. 1 W h = 3600J(1)
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(ii) Calculate the maximum charge that the battery can provide.(2)
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(iii) The mobile phone 'runs out of charge'.
Calculate the minimum time taken, in hours, for the battery to fully recharge.charging current = 0.90 A(3)
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Minimum time = ........................................................... hours
(Total for question = 6 marks)Q24.A mobile phone is powered by a lithium-ion battery. The information shown is taken from the battery.
The mobile phone, when purchased, was supplied with a charging plug marked 1 A, 5V. The mobile phone owner lost the original charging plug and replaced it with a charging plug marked 0.5 A, 5 V.
By evaluating the information given, discuss the suitability of using the replacement charging plug for this mobile phone. Include references to possible benefits, disadvantages and risks associated with using the replacement charging plug.
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(Total for question = 4 marks) Q25.A student set up a circuit containing a light dependent resistor (LDR) in series with a fixed resistor as shown.
As the student moved a lamp towards the circuit she observed the potential difference (p.d.) changing across the fixed resistor.
With reference to the electrons in the LDR explain this observation.
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(Total for question = 5 marks) Q26.The current through a wire of cross-sectional area A is I when the drift velocity of the electrons in the wire is v and the charge carrier density is n.
The wire is replaced with a wire of a different metal with half the charge carrier density but the same
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cross-sectional area A.If the current in the new wire is 2I, the drift velocity is
A v/2
B v
C 2v
D 4v
(Total for question = 1 mark)Q27.A student investigates how the current through a filament light bulb varies with the potential difference across it.
(a) Draw a diagram of a circuit the student could use to obtain suitable measurements for a range of potential difference from 0 V to 12 V.
(3)
(b) The student's results are shown on the graph.
The student decides to draw a tangent to the curve at a potential difference of 6 V and use the gradient of the tangent to determine the resistance of the bulb.(i) Explain why this is not a correct method to determine the resistance.
(2)
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(ii) Calculate the resistance of the bulb when the potential difference across it is 6 V.(2)
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*(c) Describe and explain the change in the resistance of the bulb as the potential difference across it is increased.
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(Total for question = 11 marks)
Q28.The diagram shows a current I flowing through a sample of material of length l and cross-sectional area A.The drift velocity of the free electrons is v.If the area and length are both doubled, but the current remains
the same, the drift velocity will be
A v / 4
B v / 2
C 2v
D 4v (Total for Question = 1 mark)
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Q29.Which of the following current-potential difference (I-V) graphs correctly shows the behaviour of a diode?
A
B
C
D
(Total for question = 1 mark)
Q30.Which of the following current – potential difference (I–V) graphs shows the correct behaviour for a filament bulb?
A
B
C
D (Total for Question = 1 mark)Q31.An electron is accelerated from rest through a potential difference of 5.0 kV.
The kinetic energy gained by the electron is A 8.0 × 10−16 J B 8.0 × 10−19 J C 3.2 × 10−20 J D 3.2 × 10−23 J
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(Total for question = 1 marks)Q32.A torch uses a 1.5 V dry cell. Over time, the light intensity produced by the torch decreases as the cell 'goes flat'.
Student A sets up the following circuit in an attempt to measure the e.m.f. of a cell.
Explain why the voltmeter reading will not be the e.m.f. of the cell.
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(Total for question = 2 marks) Q33.A series circuit consists of two resistors with resistances R1 and R2 and a battery of potential difference V.
Which of the following gives the potential difference across the resistor with resistance R2?
(1)
(Total for question = 1 mark)Q34.The diagram shows a uniform wire XY across which a potential difference V0 is applied.
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Which of the following correctly shows the output potential difference across XZ?
(Total for Question = 1 mark)Q35.A combination of resistors is connected to a 12 V supply of negligible internal resistance.
The potential difference between points A and B is A 4 V B 6 V C 8 V D 12 V
(Total for question = 1 marks)Q36.A student set up a circuit containing a light dependent resistor (LDR) in series with a fixed resistor as shown.
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When the lamp was at a distance of 10 cm from the LDR, the reading on the voltmeter was 2.4V.
Calculate the resistance of the LDR at this distance.
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Resistance of the LDR = ...........................................................
(Total for question = 3 marks) Q37.A current of 0.2 A flows through a lamp for 3 hours.The total charge passing through the lamp in this time is
A 2160 C
B 600 C
C 36 C
D 0.6 C (Total for Question = 1 mark)Q38.A rechargeable AA cell is labelled 2.0 Ah (ampere hours), 1.2 V.(a) Show that Ah is a unit of charge.
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(b) When charging the cell, the current is 0.19 A and the potential difference is 1.5 V for 10 hours.Calculate the electrical energy supplied while the cell is being charged.
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(c)The maximum charge that can be delivered from a fully charged cell is 7200 C.
Calculate the maximum energy which could be transferred by the cell if the output potential difference remained constant at 1.2 V.
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(d) Calculate the efficiency of the charging process.
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............................................................................................................................................. (Total for Question = 8 marks)Q39.A medical scanner uses a moving table to position the patient. Strain gauges are used to monitor the shape of the table which enables a more precise positioning of the patient.
Strain gauges consist of a thin length of wire attached, in a zigzag pattern, to a small flexible piece of plastic. The strain gauge is attached to the table. When the table is subjected to forces, the dimensions of the plastic change. This causes a change in the length of the wire and hence a change in the resistance of the wire.
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(a) Resistance can be measured directly using an ohmmeter or indirectly using measurements from a voltmeter and ammeter.
Describe two benefits of using an ohmmeter compared to using a voltmeter and an ammeter.(2)
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(b) The diagram shows forces applied to a strain gauge. The 'width' of the strain gauge is defined by the distance w.
(i) State and justify how the applied forces change the resistance of the wire.(2)
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(ii) The gauge factor GF of a strain gauge is given by
where ε is the strain, R is the initial resistance ,ΔR is the change in resistanceWhen forces are applied to the strain gauge, the resistance of the gauge changes by 0.10%.Calculate the change in the width of the strain gauge. w = 5.0 cm ,GF = 2.0
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(c) Explain the benefit of arranging the wire in a zigzag pattern.
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(Total for question = 9 marks)Q40.A copper wire of length 2.5 m and cross-sectional area 2.4 × 10−7 m2 has a resistivity of 1.7 × 10−8 Ω m
What is the resistance of the wire?
A 1.6 × 10−15 Ω
B 1.0 × 10−14 Ω
C 0.18 Ω
D 5.6 Ω
(Total for question = 1 mark)Q41.A strain gauge measures changes in the resistance of a metal under strain to find the applied force. The kitchen balance in the photograph uses strain gauges to measure the weight of cooking ingredients.
A student tests this method by measuring the resistance of a wire before a force is applied and while it is under
tension.
(a) Calculate the initial resistance of the wire.
length of wire =1.0 m, cross sectional area of wire = 2.9 × 10−8 m2
resistivity of wire = 4.9 × 10−7 Ω m
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(b) The student applies a force to the wire and measures the new length. He calculates the increase in the resistance to be 0.035 Ω. He measures the increase in resistance and finds it to be 0.070 Ω.
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The student suggests that the difference between these two values is because the cross-sectional area of the wire changes under strain.
Explain why a change in cross-sectional area would cause this difference.
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............................................................................................................................................. (Total for Question = 5 marks)Q42.A student carried out a series of measurements to determine how the resistance of a wire varies with its length.
The student obtained the following results.
The student plotted the results on a graph.
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(a) Calculate the resistivity of the wire used.cross-sectional area of wire = 1.06 × 10−7 m2
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(b)One precaution taken by the student was to keep the current small.Explain why this precaution was necessary.
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(c) Explain one other precaution which should be taken by the student to ensure the accuracy of the results in the table.
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............................................................................................................................................. (Total for Question = 8 marks)Q43.The photograph shows a piece of apparatus in which a mains light bulb and a torch bulb are both connected to the mains.
Students were surprised to see both bulbs shining normally when the apparatus was switched on.
It is impossible to tell from looking at the apparatus whether the bulbs are connected in series or in parallel.
To test this, the apparatus was switched off and the mains bulb was removed. When it was switched on again the torch bulb did not light up. When this was repeated, removing the torch bulb, the mains bulb did not light up.
When the circuit was tried again with both bulbs, they still operated normally.
(a) Complete the circuit diagram to show how the bulbs are connected and explain why they must be connected in this way and not the alternative.
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(b) The mains bulb is marked 40 W, 230 V.
(i) Show that the current in the mains bulb is about 0.2 A when it is operating normally.
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(ii) Calculate the resistance of the mains bulb when it is operating normally.
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(iii)The torch bulb is marked 2.5 V, 0.20 A.Calculate the resistance of the torch bulb when it is operating normally.
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............................................................................................................................................. (c) Explain, with reference to both current and potential difference, why it is possible to operate both bulbs at the same time from the same power supply.
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(d) Earlier in the question you were asked to calculate the resistances of the bulbs when operating normally.Explain the effect on the resistances of the bulbs if they are operated at a much smaller current so that neither bulb lights up.
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(Total for Question = 15 marks)Q44.Explain why an ammetermust be placed in series to measure current through a component
must have a very low resistance. (3) .............................................................................................................................................
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............................................................................................................................................. (Total for Question = 3 marks)Q45.Read the following extract and then answer the questions that follow.
Powdery dust, the by-product of fearsome meteor storms that pounded the Moon, coats much of the lunar surface. A build-up of this dust could damage sensitive machinery.
Scientists theorise that lunar dust must be electrostatically charged by ultraviolet solar radiation from the Sun. When ultraviolet radiation hits the Moon's "day side", the half that faces the Sun, it knocks electrons out of atoms in the lunar soil.
(a)Describe the particle model of ultraviolet radiation that explains how it can "knock electrons out of atoms".
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(b) A teacher uses the arrangement below to demonstrate that electrons can be knocked out of a metal surface in a photocell by visible light.
The arrangement can also be used to measure the maximum kinetic energy of these electrons.
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(i) Explain how the potential divider circuit can produce a range of values from 0 to 1.5 V on the voltmeter.
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(ii) The potential difference on the voltmeter is increased until the ammeter reading is zero.The voltmeter reads 0.6 V at this instant. State the maximum kinetic energy of the electrons in eV.
(1) Maximum kinetic energy = ........................................................... eV
(c) Discuss whether the photocell arrangement in part (b) gives a valid demonstration of how dust particles become charged on the Moon.
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(Total for question = 11 marks) Q46.A student set up a circuit containing a light dependent resistor (LDR) in series with a fixed resistor as shown.
The student wants to modify the circuit so that a light bulb lights up when the room goes dark.
She modifies the circuit as shown below. When working normally the resistance of the light bulb is 3Ω and the p.d. across it is 3V.
Explain, without further calculation, whether this circuit would work as intended.
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(Total for question = 3 marks)
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Q47.An ampere can be expressed as A C s−1
B J C−1
C V W−1
D V Ω(Total for question = 1 marks)
Q48.Which of the following is a correct unit for resistance?
A J C−1
B V C−1 s−1
C J C−2 s
D J C−2 s−1
(Total for question = 1 mark)Q49.The instruction booklet for an electric garden shredder includes the following advice.
(a) Describe the relationship between area and length in the table.
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(b) The cable for the shredder contains two conductors in series, the live wire and the neutral wire. A cable of length 40 m has a total conductor length of 80 m.
(i) Show that the resistance of a copper conductor of length 80 m and cross-sectional area 1.00 mm2 is about 1.3 Ω.resistivity of copper = 1.68 × 10−8 Ω m
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(ii) When in use the current for the shredder is 11 A. Calculate the rate of energy dissipation by the 40 m, 1.00 mm2 cable when it is used with the shredder.
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(iii) Calculate the total potential difference across the conductors in the 40 m cable when it is used with the shredder.
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.............................................................................................................................................(c) Suggest why the advice in the instruction booklet is included.
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(Total for question = 9 marks) Q50.A thermistor has a negative temperature coefficient. With reference to the equation I = nqvA, explain what happens to the resistance of the thermistor when its temperature increases.
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(Total for question = 3 marks)Q51.A student carried out an experiment to investigate the current-potential difference characteristics of a diode using the circuit below.
He plotted the graph of potential difference V on the y-axis against the corresponding current I on the x-axis.Which graph would be obtained by the student?
(1)
(Total for question = 1 mark)
Q52.A student set up the circuit below and moved a sliding contact along a uniform conducting wire.
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The student recorded the potential difference V across each length of wire l under test.
Which graph correctly shows how V varies with l?
(1)
(Total for question = 1 mark)
Q53.The graph shows how potential difference V varies with current I for a circuit component.
Which of the following could be the circuit component?
A copper wire
B filament lamp
C fixed resistor
D thermistor
(Total for question = 1 mark)
Q54.Which of the following expresses the volt in SI base units?
A kg m2 s−2 C−1
B kg m2 s−3 C
C kg m2 s A−1
D kg m2 s−3 A−1
(Total for question = 1 mark)
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