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Units and Measurements question

2025 · 22 Jan · Shift 2 · Q55
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Units and Measurements question

2025 · 22 Jan · Shift 2 · Q55

JEE MainPhysicsUnits and MeasurementsMCQ+4 / −1
The maximum percentage error in the measurment of density of a wire is [Given, mass of wire =(0.60±0.003)g=(0.60 \pm 0.003) \mathrm{g}=(0.60±0.003)g radius of wire =(0.50±0.01)cm=(0.50 \pm 0.01) \mathrm{cm}=(0.50±0.01)cm length of wire =(10.00±0.05)cm]=(10.00 \pm 0.05) \mathrm{cm}]=(10.00±0.05)cm]
  1. A
    7
  2. B
    8
  3. C
    5
  4. D
    4
View written solutionFree

Correct answer: C

  1. Write the formula for density

For a wire (cylindrical shape),

ρ=mV=mπr2l\rho = \frac{m}{V} = \frac{m}{\pi r^2 l}ρ=Vm​=πr2lm​

So,

ρ∝mr2l\rho \propto \frac{m}{r^2 l}ρ∝r2lm​

  1. Use maximum fractional error rule

If

ρ=mπr2l\rho = \frac{m}{\pi r^2 l}ρ=πr2lm​

then maximum relative error is

Δρρ=Δmm+2Δrr+Δll\frac{\Delta \rho}{\rho} = \frac{\Delta m}{m} + 2\frac{\Delta r}{r} + \frac{\Delta l}{l}ρΔρ​=mΔm​+2rΔr​+lΔl​

(Note: π\piπ is a constant, so it has no error.)

  1. Calculate percentage error in each quantity
  • For mass:

Δmm=0.0030.60=0.005=0.5%\frac{\Delta m}{m} = \frac{0.003}{0.60} = 0.005 = 0.5\%mΔm​=0.600.003​=0.005=0.5%

  • For radius:

Δrr=0.010.50=0.02=2%\frac{\Delta r}{r} = \frac{0.01}{0.50} = 0.02 = 2\%rΔr​=0.500.01​=0.02=2%

Since radius is squared, contribution becomes:

2×2%=4%2 \times 2\% = 4\%2×2%=4%

  • For length:

Δll=0.0510.00=0.005=0.5%\frac{\Delta l}{l} = \frac{0.05}{10.00} = 0.005 = 0.5\%lΔl​=10.000.05​=0.005=0.5%

  1. Add the maximum percentage errors

Maximum percentage error in density=0.5%+4%+0.5%=5%\text{Maximum percentage error in density} = 0.5\% + 4\% + 0.5\% = 5\%Maximum percentage error in density=0.5%+4%+0.5%=5%

  1. Match with options

5%5\%5% corresponds to Option C.

  1. Compare with stored correct answer

Stored correct answer = C

My derived answer = C

So they agree.

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