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Date May 2015 Marks available 1 Reference code 15M.3.HL.TZ2.5
Level Higher level Paper Paper 3 Time zone Time zone 2
Command term Determine Question number 5 Adapted from N/A

Question

This question is about Hubble’s law.

A galaxy a distance d away emits light of wavelength λ. Show that the shift in wavelength Δλ, as measured on Earth, is given by
Δλ=H0dλc
where H0 is the Hubble constant.

[1]
a.

Light of wavelength 620 nm is emitted from a distant galaxy. The shift in wavelength measured on Earth is 35 nm. Determine the distance to the galaxy using a Hubble constant of 68 km s–1Mpc–1.

[1]
b.

Markscheme

combining Δλλ=vc and v=H0d;
Answer given, check working.

 

 

a.
d=cΔλλH0=(3×105×35620×68);

(mark is for rearrangement)
d=250(Mpc) or 7.7×1024 (m);
Allow only first marking point if incorrect value for λ is used.
Award
[2] for a bald correct answer.

b.

Examiners report

In part (a) there were almost no incorrect answers.

a.

In part (b) far too many candidates lost 1 mark because they used the wrong power of ten for velocity in Hubble’s constant.

b.

Syllabus sections

Option D: Astrophysics » Option D: Astrophysics (Core topics) » D.3 – Cosmology
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