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JEE Main 2019 (8 Apr, Shift 2) · Errors in Measurement

Errors in Measurement question from JEE Main 2019 (8 Apr, Shift 2)

Q96JEE Main 2019 · 8 APR · SHIFT 2Difficult

Errors in Measurement

In a simple pendulum experiment for determination of acceleration due to gravity (g), time taken for 20 oscillations is measured by using a watch of 1 second least count. The mean value of time taken comes out to be 30 s. The length of pendulum is measured by using a meter scale of least count 1 mm and the value obtained is 55.0 cm. The percentage error in the determination of g is close to :-

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Answer: (d)

  1. g=4π2lT2g = \frac{4\pi^2 l}{T^2} with T=t/20T = t/20, so Δgg=Δll+2Δtt\frac{\Delta g}{g} = \frac{\Delta l}{l} + 2\frac{\Delta t}{t}
  2. Δll=0.155.0=0.18%\frac{\Delta l}{l} = \frac{0.1}{55.0} = 0.18\%
  3. 2Δtt=2(130)=6.67%2\frac{\Delta t}{t} = 2\left(\frac{1}{30}\right) = 6.67\%
  4. Total ≈6.85%≈6.8%\approx 6.85\% \approx 6.8\%
  5. So the answer is (d) 6.8%6.8\%.
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