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4.3 Electric circuits

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Question 32

A student investigates the resistance of combinations of three resistors, RAR_{\text{A}}RA​, RBR_{\text{B}}RB​, and RCR_{\text{C}}RC​.

They first connect resistor RAR_{\text{A}}RA​ to a power supply with a switch and an ammeter in series, and a voltmeter in parallel across RAR_{\text{A}}RA​.

a.

With the switch closed, the student records:

V1=2.4 V V_1 = 2.4\text{ V} V1​=2.4 V I1=0.20 A I_1 = 0.20\text{ A} I1​=0.20 A

Calculate the resistance R1R_1R1​ of resistor RAR_{\text{A}}RA​.

[2]
b.

The student then connects RBR_{\text{B}}RB​ in series with RAR_{\text{A}}RA​, keeping the voltmeter connected across both resistors. They record:

V2=2.4 V V_2 = 2.4\text{ V} V2​=2.4 V I2=0.11 A I_2 = 0.11\text{ A} I2​=0.11 A

Calculate the combined resistance R2R_2R2​ of RAR_{\text{A}}RA​ and RBR_{\text{B}}RB​.

[1]
c.

Finally, the student connects RCR_{\text{C}}RC​ in series with RAR_{\text{A}}RA​ and RBR_{\text{B}}RB​, keeping the voltmeter connected across all three resistors. They record:

V3=2.4 V V_3 = 2.4\text{ V} V3​=2.4 V I3=0.07 A I_3 = 0.07\text{ A} I3​=0.07 A

Calculate the combined resistance R3R_3R3​ of all three resistors in series.

[1]
d.

A student suggests that R3=3×R1R_3 = 3 \times R_1R3​=3×R1​. State whether the experimental results support this suggestion. Justify your answer by comparing the values with reference to an experimental accuracy limit of 10%10\%10%.

[3]
e.

Explain how the student could use the original circuit setup to verify that all three resistors have the same value of resistance.

[2]
f.

The student wants to redesign the experiment to measure the combined resistance of the three resistors connected in parallel. Describe how the circuit should be modified, specifying:

  1. how the three resistors should be connected relative to one another,
  2. where the voltmeter should be connected,
  3. where a variable resistor (rheostat) should be connected to control the current in all three resistors.
[3]
g.

Suggest a reason for connecting a variable resistor in this circuit.

[1]
Markscheme

4.3 Electric circuits Questions

  1. IGCSE
  2. /Physics
  3. /4.3 Electric circuits

136 exam-style questions on CIE IGCSE Physics 4.3 Electric circuits, covering 4.3.1a Circuit diagrams and circuit components, 4.3.2a Series circuits, 4.3.2b Parallel circuits, 4.3.2c Current and potential difference in circuits, 4.3.2d Combined resistance of resistors in parallel, and 4.3.3 Action and use of circuit components. Each one has a worked solution and a mark scheme showing where the marks go.

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