arthham

JEE Advanced 2004 · Units and Measurements

A wire of length ℓ=6±0.06 cm\ell = 6 \pm 0.06\,\text{cm} and radius r=0.5±0.005 cmr = 0.5 \pm 0.005\,\text{cm} and mass m=0.3±0.003 gmm = 0.3 \pm 0.003\,\text{gm}. Maximum percentage error in density is

Answer: A. 44

Watch this solved on the board The full walkthrough, written out a line at a time with narration explaining each step as it appears. Pause anywhere and ask why a line is there. Free to watch

Or read the worked solution below. Jump to the steps ↓

Written solution

Step 1: Identify the given values.

The measurements and their absolute errors are:

ℓ=6±0.06 cm\ell = 6 \pm 0.06\ \text{cm} r=0.5±0.005 cmr = 0.5 \pm 0.005\ \text{cm} m=0.3±0.003 gmm = 0.3 \pm 0.003\ \text{gm}

Step 2: Write the formula for density and its relative error.

The density ρ\rho of a cylindrical wire is given by:

ρ=mπr2ℓ\rho = \frac{m}{\pi r^2 \ell}

Taking the natural logarithm on both sides:

ln⁡ρ=ln⁡m−2ln⁡r−ln⁡ℓ−ln⁡π\ln\rho = \ln m - 2\ln r - \ln \ell - \ln\pi

Differentiating to find the maximum fractional error:

Δρρ=Δmm+2Δrr+Δℓℓ\frac{\Delta\rho}{\rho} = \frac{\Delta m}{m} + 2\frac{\Delta r}{r} + \frac{\Delta \ell}{\ell}

Step 3: Calculate the individual percentage errors.

For mass mm:

Δmm×100%=0.0030.3×100%=1%\frac{\Delta m}{m} \times 100\% = \frac{0.003}{0.3} \times 100\% = 1\%

For radius rr:

2(Δrr)×100%=2×0.0050.5×100%=2%2\left(\frac{\Delta r}{r}\right) \times 100\% = 2 \times \frac{0.005}{0.5} \times 100\% = 2\%

For length ℓ\ell:

Δℓℓ×100%=0.066×100%=1%\frac{\Delta \ell}{\ell} \times 100\% = \frac{0.06}{6} \times 100\% = 1\%

Step 4: Calculate the maximum percentage error in density.

Sum the individual percentage errors:

Δρρ×100%=1%+2%+1%\frac{\Delta\rho}{\rho} \times 100\% = 1\% + 2\% + 1\% Δρρ×100%=4%\frac{\Delta\rho}{\rho} \times 100\% = 4\%

Answer: The maximum percentage error in density is 4%4\% (Option 1).

More from Units and Measurements

All 37 Units and Measurements questions →

Units and Measurements: formulas and what the chapter covers →