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IGCSEPhysicsCambridge (CIE)Exam Questions4. Electricity & MagnetismElectric Circuits & Electrical Safety

Electric Circuits & Electrical Safety (Cambridge (CIE) IGCSE Physics)

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17 marks

A student investigates a wind turbine, which is an electrical generator driven by a propeller blade.

Plan an experiment which will enable him to investigate how the current in a resistor connected across the terminals of the turbine varies with the speed of the air flow through the turbine.

The apparatus available includes:

a model wind turbine as shown in Fig. 4.1

an electric fan to provide the moving air to turn the turbine

a device for measuring air speed.

In your plan, you should:

  • list any additional apparatus needed

  • complete the wind turbine circuit diagram on Fig. 4.1

  • state the key variables to be kept constant

  • explain briefly how to carry out the experiment, including how the speed of the air flow is to be changed

  • explain how to use the readings to reach a conclusion.

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2a4 marks

A student determines the resistances of some filament lamps.

Fig. 2.1 shows the first circuit she uses. 

p6-circuit

(i) Record the potential difference V subscript 1 across the lamp L1, as shown on the voltmeter in Fig. 2.2.

p6-meters

                                     

V subscript 1 = .................................................. V [1]

(ii) Record the current I subscript 1 in the circuit, as shown in Fig. 2.3.

    

    

I subscript 1 = .................................................. A [1]

      

     

(iii) Calculate the resistance R subscript 1 of the filament of lamp L1. Use the equation R subscript 1 equals V subscript 1 over I subscript 1 . Include the unit.

                           

R subscript 1 = ..................................................... [2]

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2b1 mark

The student disconnects the voltmeter. She connects lamp L2 in series with lamp L1. She connects the voltmeter across lamp L2.

         She measures the current I subscript 2 in the circuit and the potential difference V subscript 2 across lamp L2.

          I subscript 2 = ..... 0.30 A ..... V subscript 2 = ..... 1.7 V .....

Calculate the resistance R2 of the filament of lamp L2. Use the equation R subscript 2 equals V subscript 2 over I subscript 2.

R subscript 2 = .............................................

The student disconnects the voltmeter. She connects lamp L3 in series with lamps L1 and L2. She connects the voltmeter across lamp L3.

She measures the current I subscript 3 in the circuit and the potential difference V subscript 3 across lamp L3.            

I subscript 2 = ..... 0.26 A ..... V subscript 2 = ..... 1.2 V .....

     

Calculate the resistance R3 of the filament of lamp L3. Use the equation R subscript 3 equals V subscript 3 over I subscript 3.

R subscript 3 = ...................................

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2c1 mark

Calculate R1 + R2 + R3. Give your answer to a suitable number of significant figures for this experiment.

    

    R1 + R2 + R3 = ..................................................... 

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2d2 marks

Some students make suggestions about the results of the experiment.

Suggestion A:  R1 + R2 + R3 should be equal to 3 × R1

Suggestion B:  R1 + R2 + R3 should be less than 3 × R1

Suggestion C:  R1 + R2 + R3 should be greater than 3 × R1

State which suggestion A, B or C agrees with your results. Justify your answer by reference to your results.

2e3 marks

Draw a circuit diagram to show the circuit used in part (b) with all three lamps connected in series.

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3a1 mark

A student is investigating a circuit containing different lamps. She is using the circuit shown in Fig. 3.1.

atp-4

On Fig. 3.1, draw a voltmeter connected so that it measures the potential difference (p.d.) across lamp X.

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3b1 mark

The student uses the ammeter to measure the current in the circuit.

 

atp-5

 

Record the current IS in amperes, A, in the circuit, as shown in Fig. 3.2.

IS = ............................................................

3c4 marks

(i) The student uses the voltmeter to measure the p.d. VX across lamp X and then reconnects the voltmeter to measure the p.d. VY across lamp Y.

 

atp-6

 

Record the value of the p.d. VX  across lamp X, shown in Fig. 3.3.

VX  = ...............................................................

Record the value of the p.d. VY across lamp Y, shown in Fig. 3.4.

VY  = ............................................................... [1]

(ii) She then measures the p.d. VS across both lamps in series.

 

atp-7

 

Record the value of the p.d. VS across both lamps in series, shown in Fig. 3.5.

 

VS  = ...............................................................[1]

(iii) A student suggests that VS should be equal to (VX + VY). State whether the readings support this suggestion. Justify your statement with reference to the results.

[2]

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3d1 mark

Calculate the resistance R1 of lamp X. Use the readings from (b) and (c)(i) and the equation

R subscript 1 space equals space V subscript X over I subscript S.

 

R1 = ......................................................Ω .

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3e4 marks

Extended tier only

(i) The circuit components are to be rearranged so that

  • lamps X and Y are connected in parallel

  • the ammeter measures the current in lamp X only

  • the voltmeter measures the p.d. across the lamps.

Draw a circuit diagram of this arrangement.

[2]

(ii) The student sets up the circuit as described in (e)(i).

 She measures and records the current in lamp X and the p.d. across the lamps.

 She then calculates a new resistance R2 for lamp X in this parallel circuit.

 R2 = 8.3 Ω

 The student notices that lamp X is very bright in this parallel circuit, but it was dim in the series circuit in (a).

Suggest how temperature affects the resistance of a lamp. Justify your suggestion by reference to the value of R1 from (d) and the value of R2.

[2]

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