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4.2 Electrical quantities

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Question 82

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 Electrical quantities Questions

  1. IGCSE
  2. /Physics
  3. /4.2 Electrical quantities

452 exam-style questions on CIE IGCSE Physics 4.2 Electrical quantities, covering 4.2.1a Positive and negative charge, 4.2.1b Charging by friction and detecting charge, 4.2.1c Electrical conductors and insulators, 4.2.1d Electric fields and electric field patterns, 4.2.2a Electric current, charge and measuring current, 4.2.2b Conduction in metals and the direction of current, 4.2.2c Direct current and alternating current, 4.2.3a Electromotive force, 4.2.3b Potential difference and voltmeters, 4.2.4a Resistance, 4.2.4b Resistance of a metallic wire, 4.2.4c Current–voltage graphs, and 4.2.5 Electrical energy and electrical power. Each one has a worked solution and a mark scheme showing where the marks go.

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