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Question 20N.3.HL.TZ0.7

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Date November 2020 Marks available [Maximum mark: 5] Reference code 20N.3.HL.TZ0.7
Level HL Paper 3 Time zone TZ0
Command term Calculate, Explain Question number 7 Adapted from N/A
7.
[Maximum mark: 5]
20N.3.HL.TZ0.7

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

(a)

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

[1]

Markscheme

«∆ff=g∆hc2=9.81×22.6c2»∆ff=2.46×10-15 ✓

Examiners report

The calculation was easily done by most candidates.

(b(i))

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

[2]

Markscheme

GPE gained by photons so E increases ✓

E=hf, so frequency increases ✓

Examiners report

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

(b(ii))

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]

Markscheme

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.

Examiners report

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

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