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MHT CET202520 Apr 2025Evening ShiftPhysicsWaves and SoundActual

The apparent wavelength of light from a star moving away from the earth is 0.02 % more than the actual wavelength. The velocity of star is [ c = . velocity of light .=3 10^8 ~m / s ]

Options

  1. A30 ~km / s
  2. B60 ~km / s
  3. C90 ~km / s
  4. D120 ~km / s

Correct answer

B. 60 ~km / s

Step-by-step solution

Doppler effect analysis: The apparent wavelength is 0.02 % greater than the actual wavelength, giving = 0.0002 . For a receding light source, the relativistic Doppler shift formula simplifies to = v c when v c . Substituting values: v c = 0.0002 v = 0.0002 3 10^8 m/s = 6 10^4 m/s Converting to kilometers per second: v = 60 km/s This result corresponds to option B .

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