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JEE Main 2022 (26 Jun, Shift 2) · Wave Theory, Wavefronts & Doppler Effect

Wave Theory, Wavefronts & Doppler Effect question from JEE Main 2022 (26 Jun, Shift 2)

Q16JEE Main 2022 · 26 JUN · SHIFT 2Medium

Wave Theory, Wavefronts & Doppler Effect

For a specific wavelength 670 nm of light coming from a galaxy moving with velocity v, the observed wavelength is 670.7 nm. The value of v is:

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Answer: (c)

  1. Doppler shift: v=cΔλλv = c\dfrac{\Delta\lambda}{\lambda}, with Δλ=670.7−670=0.7\Delta\lambda = 670.7 - 670 = 0.7 nm.
  2. v=3×108×0.7670≈3.13×105v = 3\times10^{8} \times \dfrac{0.7}{670} \approx 3.13\times10^{5} m/s (galaxy receding).
  3. So the answer is (c) 3.13×1053.13\times10^{5} m/s.
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