COSMIC MICROWAVE BACKGROUND (CMB) RADIATION

3 marks · Normal

Light from a galaxy is measured, and the absorption lines are found to be shifted by 200 nm compared to the reference wavelength of 500 nm on Earth.

(a)

Calculate the velocity of the galaxy relative to Earth. (Speed of light = 3.0 × 10^8 m/s)

[2 marks]

(b)

State whether the galaxy is moving towards or away from Earth.

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) 1.2 × 10^8 m/s

(b) Away

Common mistakes: dividing by 200 instead of 500; wrong direction for movement

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Marking points

M1 (a) · 1 mark · Correctly substitutes values into the Doppler equation. (follow-through)

A1 (a) · 1 mark · Carries out the calculation and gives answer with correct unit.

B1 (b) · 1 mark · States moving away from Earth.

Worked solution

Since the absorption line is shifted to a longer wavelength, the galaxy is moving away from Earth.