End of Chapter Assessment – Electric current

Name: ________________________

Class: ________________________

Date: ________________________

Time: 60 minutes

Marks: 50 marks

/50 %

Page 1 of 11
Q1.
A student connects four lamps A, B, C and D in the circuit shown in Figure 1.
The battery has an emf of 9.0 V and negligible internal resistance.

Figure 1

(a) The table shows the operating conditions for the lamps when they are at normal
brightness.

Lamps Operating voltage / V Power / W

A and C 6.0 6.0

B and D 3.5 4.1

The student observes that two of the lamps are at their normal brightness.
Assume that any changes in resistance of the lamps are negligible. Determine which
two lamps are at their normal brightness. Use calculations to support your answer.

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(4)

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(b) The student connects another lamp E in the circuit as shown in Figure 2.
Lamp E is identical to lamps A and C.

Figure 2

Explain what the student would observe regarding the brightness of the lamps.

Refer to potential differences across lamp E in your answer.

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(3)

(c) Lamp B in Figure 2 fails so that it no longer conducts. This change does not affect
the resistance of the other lamps. Deduce the effect on the current in the battery.
Use calculations to support your answer.

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(3)
(Total 10 marks)

Page 3 of 11
Q2.
The diagram shows a circuit designed by a student to monitor temperature changes.

The supply has negligible internal resistance and the thermistor has a resistance of 750 Ω
at room temperature. The student wants the output potential difference (pd) at room
temperature to be 5.0 V

(a) The 0.25 kΩ resistor is made of 50 turns of wire that is wound around a non-
conducting cylinder of diameter 8.0 mm.

Resistivity of the wire = 4.2 × 10 –7 Ω m.

Determine the area of cross-section of the wire that has been used for the resistor.

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(3)

(b) The student selects a resistor rated at 0.36 W for the 0.25 kΩ resistor in the
diagram. Determine whether this resistor is suitable.

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(2)

Page 4 of 11
(c) Determine the value of R that the student should select.

Give your answer to an appropriate number of significant figures.

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(5)

(d) State and explain the effect on the output pd of increasing the temperature of the
thermistor.

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(2)
(Total 12 marks)

Page 5 of 11
Q3.
The graph below shows the current–voltage (I–V) characteristics for a resistor and a
filament lamp.

(a) Explain, in terms of electron motion, why the I–V characteristic for the filament lamp
is a curve.

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(4)

(b) Determine the resistance of the resistor.

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(1)

Page 6 of 11
(c) The resistor and the filament lamp are connected in series with a supply of variable
emf and negligible internal resistance.

Determine the emf that produces a current of 0.18 A in the circuit.

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(3)

(d) The resistor and filament lamp are now connected in parallel. Determine the
resistance of the parallel combination when the emf of the supply is adjusted to be
4.0 V.

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(3)

(e) The resistance of the filament lamp at its working temperature is 14 Ω. The filament
has a length of 0.36 m and a diameter of 32 µm.

Calculate the resistivity of the metal that is used for the filament when the lamp is at
its working temperature. Give an appropriate unit for your answer.

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(3)
(Total 14 marks)

Page 7 of 11
Q4.
(a) State what is meant by a superconducting material.

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(2)

(b) State an application of a superconductor and explain why it is useful in this

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(2)
(Total 4 marks)

Page 8 of 11
Q5.
Figure 1 shows the current–voltage (I−V) characteristic of the lamp used in a car
headlight up to its working voltage.

Figure 1

(a) Draw on Figure 1 the characteristic that would be obtained with the connections to
the supply reversed.

(2)

(b) Lamps are marked with their working voltage and the power used at this voltage.
For example, a lamp for use in a torch may be marked 2.5 V 0.3 W. Deduce the
marking on the lamp for the car headlight.

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(2)

(c) Determine the resistance of the lamp when the potential difference (pd) across it is

Page 9 of 11
 half the working voltage.

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(1)

(d) Explain, without further calculation, how the resistance of the lamp varies as the
voltage across it is increased from zero to its working voltage.

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(3)

(e) A student suggests that the circuit shown in Figure 2 is suitable for collecting data
to draw the I−V characteristic of the lamp up to its working voltage. The maximum
resistance of the variable resistor is 6.0 Ω and the internal resistance of the power
supply is 2.0 Ω. The resistance of the ammeter is negligible.

Figure 2

Discuss the limitations of this circuit when used to collect the data for the
characteristic.

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(2)
(Total 10 marks)

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Page 11 of 11