If a star emitting yellow light is accelerated towards earth, then to an observer on earth it will appear (a) becoming orange. (b) shining yellow. (c) gradually changing to blue. (d) gradually changing to red.

Answer: (c). For a source approaching the observer, Δλ = -λ v/c: wavelength decreases (blue shift). As the star accelerates, v keeps increasing, so the shift keeps growing. Yellow light therefore shifts gradually towards blue. So the answer is (c).

If a star emitting yellow light is accelerated towards earth, then to… | MHT CET 2019 (2 May, Shift 1)

Q20MHT CET 2019 · 2 MAY · SHIFT 1Easy

Wave Theory, Wavefronts & Doppler Effect

If a star emitting yellow light is accelerated towards earth, then to an observer on earth it will appear

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Answer: (c)

For a source approaching the observer, $\Delta\lambda = -\lambda v/c$ : wavelength decreases (blue shift).
As the star accelerates, $v$ keeps increasing, so the shift keeps growing.
Yellow light therefore shifts gradually towards blue.
So the answer is (c).

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