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MHT CET 2025 (20 Apr, Shift 2) · Wave Theory, Wavefronts & Doppler Effect

Wave Theory, Wavefronts & Doppler Effect question from MHT CET 2025 (20 Apr, Shift 2)

Q10MHT CET 2025 · 20 APR · SHIFT 2Medium

Wave Theory, Wavefronts & Doppler Effect

The apparent wavelength of light from a star moving away from the earth is 0.02%0.02\% more than the actual wavelength. The velocity of star is [c=[c = velocity of light =3×108 m/s]= 3 \times 10^{8}\text{ m/s}]

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Answer: (b)

  1. Doppler shift: Δλλ=vc\dfrac{\Delta\lambda}{\lambda} = \dfrac{v}{c}.
  2. Δλλ=0.02%=2×10−4\dfrac{\Delta\lambda}{\lambda} = 0.02\% = 2\times10^{-4}
  3. v=2×10−4×3×108=6×104v = 2\times10^{-4} \times 3\times10^{8} = 6\times10^{4} m/s =60= 60 km/s
  4. So the answer is (b) 60 km/s.
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