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JEE Main 2021 (18 Mar, Shift 1) · Errors in Measurement

Errors in Measurement question from JEE Main 2021 (18 Mar, Shift 1)

Q86JEE Main 2021 · 18 MAR · SHIFT 1Difficult

Errors in Measurement

The time period of a simple pendulum is given by T=2πlgT = 2\pi\sqrt{\frac{l}{g}}. The measured value of the length of pendulum is 10 cm known to a 1mm accuracy. The time for 200 oscillations of the pendulum is found to be 100 second using a clock of 1s resolution. The percentage accuracy in the determination of 'g' using this pendulum is 'x'. The value of 'x' to be nearest integer is :-

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Answer: (b)

  1. g=4π2lT2g = \dfrac{4\pi^2 l}{T^2}, so Δgg=Δll+2ΔTT\dfrac{\Delta g}{g} = \dfrac{\Delta l}{l} + 2\dfrac{\Delta T}{T}.
  2. Δll=0.1 cm10 cm=1%\dfrac{\Delta l}{l} = \dfrac{0.1\text{ cm}}{10\text{ cm}} = 1\%
  3. ΔTT=Δtt=1100=1%\dfrac{\Delta T}{T} = \dfrac{\Delta t}{t} = \dfrac{1}{100} = 1\%, so 2ΔTT=2%2\dfrac{\Delta T}{T} = 2\%
  4. x=1%+2%=3%x = 1\% + 2\% = 3\%, answer (b).
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