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4.2.4a Resistance

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Question 36

A student investigates how the resistance of a section of wire depends on the number of identical wires connected in parallel within that section.

The student sets up a circuit with three sections, PQPQPQ, QRQRQR, and RSRSRS, connected in series:

  • Section PQPQPQ consists of one 40 cm40\text{ cm}40 cm piece of resistance wire.
  • Section QRQRQR consists of two 40 cm40\text{ cm}40 cm pieces of resistance wire in parallel.
  • Section RSRSRS consists of three 40 cm40\text{ cm}40 cm pieces of resistance wire in parallel.

The current in the circuit is measured to be I=0.50 AI = 0.50\text{ A}I=0.50 A. The potential differences across the sections are recorded as:

  • V1V_1V1​ across PQ=1.80 VPQ = 1.80\text{ V}PQ=1.80 V
  • V2V_2V2​ across QR=0.92 VQR = 0.92\text{ V}QR=0.92 V
  • V3V_3V3​ across RS=0.61 VRS = 0.61\text{ V}RS=0.61 V
a.

(i) Calculate the resistance R1R_1R1​ of section PQPQPQ using the equation R1=V1IR_1 = \frac{V_1}{I}R1​=IV1​​. Give your answer to a suitable number of significant figures and include the unit.

[2]
b.

(ii) Calculate the resistances R2R_2R2​ and R3R_3R3​ for sections QRQRQR and RSRSRS respectively.

[2]
c.

(i) State the general relationship shown by these results between the number of wires in parallel in a section and its electrical resistance.

[1]
d.

(ii) Justify your conclusion in (b)(i) by reference to your calculated resistance values.

[1]
e.

Explain how you would modify this experiment to investigate the relationship between the length of a single piece of the resistance wire and its resistance.

[3]
Markscheme

4.2.4a Resistance Questions

  1. IGCSE
  2. /Physics
  3. /4.2.4a Resistance

132 exam-style questions on CIE IGCSE Physics 4.2.4a Resistance. Each one has a worked solution and a mark scheme showing where the marks go.

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