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Date November 2020 Marks available 1 Reference code 20N.3.HL.TZ0.7
Level Higher level Paper Paper 3 Time zone 0 - no time zone
Command term Calculate Question number 7 Adapted from N/A

Question

In the Pound–Rebka–Snider experiment, a source of gamma rays was placed 22.6m vertically above a gamma ray detector, in a tower on Earth.

Calculate the fractional change in frequency of the gamma rays at the detector.

[1]
a.

Explain the cause of the frequency shift for the gamma rays in your answer in (a) in the Earth’s gravitational field.

[2]
b(i).

Explain the cause of the frequency shift for the gamma rays in your answer in (a) if the tower and detector were accelerating towards the gamma rays in free space.

[2]
b(ii).

Markscheme

«ff=ghc2=9.81×22.6c2»ff=2.46×10-15 ✓

a.

GPE gained by photons so E increases

E=hf, so frequency increases

b(i).

gamma rays travel at c

detector accelerates towards source so «by Doppler effect» λ reduced so frequency increases

 

Award [1 max] for reference to principle of equivalence without further explanation.

b(ii).

Examiners report

The calculation was easily done by most candidates.

a.

A simple conceptual explanation in terms of the energy changes was not present.

b(i).

Some candidates did score marks although it was not as simple as anticipated for a classical question.

b(ii).

Syllabus sections

Option A: Relativity » Option A: Relativity (Additional higher level option topics) » A.5 – General relativity (HL only)
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