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Units and Measurements question

2024 · 31 Jan · Shift 1 · Q76
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Units and Measurements question

2024 · 31 Jan · Shift 1 · Q76

JEE MainPhysicsUnits and MeasurementsMCQ+4 / −1
If the percentage errors in measuring the length and the diameter of a wire are 0.1%0.1 \%0.1% each. The percentage error in measuring its resistance will be:
  1. A
    0.144%
  2. B
    0.2%
  3. C
    0.1%
  4. D
    0.3%
View written solutionFree

Correct answer: D

  1. Write the relation for resistance of a wire

    For a wire, R=ρLAR = \rho \frac{L}{A}R=ρAL​ where LLL is length and AAA is cross-sectional area.

  2. Express area in terms of diameter

    For a circular wire, A=πd24A = \frac{\pi d^2}{4}A=4πd2​ Hence, R=ρ4Lπd2R = \rho \frac{4L}{\pi d^2}R=ρπd24L​

    So, R∝Ld2R \propto \frac{L}{d^2}R∝d2L​

  3. Use percentage error formula

    For a quantity of the form R∝L1d−2R \propto L^1 d^{-2}R∝L1d−2 the maximum percentage error is ΔRR×100=ΔLL×100+2Δdd×100\frac{\Delta R}{R}\times 100 = \frac{\Delta L}{L}\times 100 + 2\frac{\Delta d}{d}\times 100RΔR​×100=LΔL​×100+2dΔd​×100

  4. Substitute the given errors

    Given: ΔLL×100=0.1%\frac{\Delta L}{L}\times 100 = 0.1\%LΔL​×100=0.1% Δdd×100=0.1%\frac{\Delta d}{d}\times 100 = 0.1\%dΔd​×100=0.1%

    Therefore, ΔRR×100=0.1+2(0.1)=0.3%\frac{\Delta R}{R}\times 100 = 0.1 + 2(0.1) = 0.3\%RΔR​×100=0.1+2(0.1)=0.3%

  5. Match with the options

    0.3%0.3\%0.3% corresponds to Option D.

  6. Comparison with stored answer

    Stored correct answer: D

    Derived answer: D

    So they agree.

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