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4.3 Electric circuits

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Question 6

A student investigates a circuit containing a parallel combination of two resistors, P P\,P and QQQ, connected in series with a resistor SSS, an ammeter to measure the total circuit current, and a power supply.

The student obtains the following experimental readings:

  • Potential difference across the parallel combination of P P\,P and QQQ: VPQ=1.8 VV_{PQ} = 1.8\text{ V}VPQ​=1.8 V
  • Potential difference across resistor SSS: VS=3.6 VV_S = 3.6\text{ V}VS​=3.6 V
  • Total current in the circuit: IT=0.45 AI_T = 0.45\text{ A}IT​=0.45 A
  • Branch current through resistor PPP: IP=0.15 AI_P = 0.15\text{ A}IP​=0.15 A
  • Branch current through resistor QQQ: IQ=0.28 AI_Q = 0.28\text{ A}IQ​=0.28 A
a.

Calculate the equivalent resistance RPQR_{PQ}RPQ​ of the parallel combination. State your answer with the appropriate unit.

[2]
b.

Calculate the resistance RS R_S\,RS​ of resistor SSS.

[2]
c.

State whether the student's results support the physical suggestion that IT=IP+IQI_T = I_P + I_QIT​=IP​+IQ​. Justify your statement by comparing the numerical values.

[2]
d.

Rather than using a variable resistor, the student suggests controlling the current by swapping resistors P P\,P and Q Q\,Q with different discrete resistors. State one disadvantage of this method.

[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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