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A star is sending out light of wavelength 5000 Å and is moving toward the Earth with a speed of 1.50 × 10⁶ m/s. What is the shift in the wavelength of the light observed on Earth?

1. 0.25 Å
2. 2.5 Å
3. 25 Å
4. 250 Å

Correct answer: 25 Å

Solution

Doppler shift: d_lambda = lambda*v/c = 5000 * (1.5e6/3e8) = 5000 * 0.005 = 25 A.

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