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JEE Mains · Physics · STD 11 - 1. units,dimensions and measurement

A student determined Young's Modulus of elasticity using the formula \(Y=\frac{M g L^{3}}{4 b d^{3} \delta} .\) The value of \(g\) is taken to be \(9.8 \,{m} / {s}^{2}\), without any significant error, his observation are as following.
Physical Quantity Least count of the Equipment used for measurement Observed value
Mass \(({M})\) \(1\; {g}\) \(2\; {kg}\)
Length of bar \((L)\) \(1\; {mm}\) \(1 \;{m}\)
Breadth of bar \((b)\) \(0.1\; {mm}\) \(4\; {cm}\)
Thickness of bar \((d)\) \(0.01\; {mm}\) \(0.4 \;{cm}\)
Depression \((\delta)\) \(0.01\; {mm}\) \(5 \;{mm}\)
Then the fractional error in the measurement of \({Y}\) is

  1. A \(0.0083\)
  2. B \(0.0155\)
  3. C \(0.155\)
  4. D \(0.083\)
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Answer & Solution

Correct Answer

(B) \(0.0155\)

Step-by-step Solution

Detailed explanation

\({y}=\frac{{MgL}^{3}}{4 {bd}^{3} \delta}\) \(\frac{\Delta {y}}{{y}}=\frac{\Delta {M}}{{M}}+\frac{3 \Delta {L}}{{L}}+\frac{\Delta {b}}{{b}}+\frac{3 \Delta {d}}{{d}}+\frac{\Delta \delta}{\delta}\)…
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