COSMIC MICROWAVE BACKGROUND (CMB) RADIATION

3 marks · Easy

Light from a distant galaxy has a wavelength of 660 nm. The same spectral line measured from our Sun is 600 nm. Calculate the speed at which the galaxy is moving relative to Earth. (Speed of light = m/s)

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.

Show answer

3.0 × 10^7 m/s (±1000000)

Must show: use of formula, correct substitution, correct answer to correct sig figs

Also accept: 3.0 × 10^7; 30,000,000 m/s

Common mistakes: using the wrong difference; incorrect rearrangement

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Correct use or writing of or rearrangement to solve for v.

M1 · 1 mark · Correct substitution of values ( nm, nm, m/s), with unit conversion if needed.

A1 · 1 mark · Correct evaluation of galaxy speed: m/s (accept 30,000,000 m/s or equivalent forms).

Worked solution

Given:

Change in wavelength:

Substitute values (no need to convert nm because they cancel):