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CAIE A-Level Physics 9.3.6 Resistivity Equation Question Bank

Practise using R = rho L/A to calculate resistance, resistivity, length or area, converting dimensions and explaining how material and geometry affect resistance.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • calculate resistance, resistivity, length, area or current-related quantities using R = ρL/A
  • rearrange R = ρL/A and convert cross-sectional dimensions or units consistently
  • interpret how material, length and cross-sectional area affect resistance and distinguish resistance from resistivity

9.3.6—R = ρL / A question 1

[Maximum number: 3]

One end of a wire is attached to a fixed point. A force F is applied to the wire to cause extension x. The variation with F of x is shown in Fig. 5.1.

Fig. 5.1

Fig. 5.1

The wire has a cross-sectional area of 4.1×10−7 m24.1 \times 10^{-7} \mathrm{~m}^{2} and is made of metal of Young modulus 1.7×1011 Pa1.7 \times 10^{11} \mathrm{~Pa}. Assume that the cross-sectional area of the wire remains constant as the wire extends.

The resistivity of the metal of the wire is 3.7×10−7Ω m3.7 \times 10^{-7} \Omega \mathrm{~m}.

Determine the change in resistance of the wire when the extension x of the wire changes from x=0.48 mmx=0.48 \mathrm{~mm} to x=0.60 mmx=0.60 \mathrm{~mm}.
change in resistance = Ω\Omega

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