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⚛️ Physics  ·  Units and Measurements  ·  NEET & JEE

A student measures the time period of a pendulum using a stopwatch with a least count of 0.1 s, timing 20 oscillations to get 36.0 s. If the same stopwatch were used to time only 5 oscillations instead, the percentage error in the measured time period would:

Answer: Increase, since the fixed instrumental error is now spread over fewer oscillations.

  • A Increase, since the fixed instrumental error is now spread over fewer oscillations
  • B Decrease, since timing fewer oscillations generally reduces human reaction-time error
  • C Stay the same, since the least count of the stopwatch is unchanged
  • D Become zero, since the period of a pendulum does not depend on the number of oscillations timed

Correct answer: A. Increase, since the fixed instrumental error is now spread over fewer oscillations

Explanation: The absolute error from the stopwatch's least count is fixed per reading, so dividing it by a smaller number of oscillations gives a larger percentage error in the period; timing more oscillations reduces this error.

The 7 SI Base UnitsLengthmetre (m)fundamentalMasskilogram (kg)Timesecond (s)Electric Currentampere (A)Temperaturekelvin (K)Amount ofSubstancemole (mol)LuminousIntensitycandela (cd)Every other physical quantity is derived by combining powers of these 7 base units

The 7 SI base units. All derived units (newton, joule, watt, volt, etc.) can be expressed as combinations of these 7 fundamental units raised to various powers.

Concept context

SI base units, dimensional analysis, significant figures, and error propagation. The toolkit every physics calculation relies on.

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