DP Physics (last assessment 2024)

Test builder »

Question 19N.3.HL.TZ0.a

Select a Test
Date November 2019 Marks available [Maximum mark: 2] Reference code 19N.3.HL.TZ0.a
Level HL Paper 3 Time zone TZ0
Command term Explain Question number a Adapted from N/A
a.
[Maximum mark: 2]
19N.3.HL.TZ0.a

A black hole has a Schwarzschild radius R. A probe at a distance of 0.5R from the event horizon of the black hole emits radio waves of frequency f that are received by an observer very far from the black hole.

Explain why the frequency of the radio waves detected by the observer is lower than f.

[2]

Markscheme

ALTERNATIVE 1
as the photons move away from the black hole, they lose energy in the gravitational field ✔
since E=hf «the detected frequency is lower than the emitted frequency» ✔

 

ALTERNATIVE 2
if the observer was accelerating away from the probe, radio waves would undergo Doppler shift towards lower frequency ✔
by the equivalence principle, the gravitational field has the same effect as acceleration ✔

 

ALTERNATIVE 3
due to gravitational time dilation, time between arrivals of wavefronts is greater for the observer ✔
since f=1T, «the detected frequency is lower than the emitted frequency» ✔

 

NOTE: The question states that received frequency is lower so take care not to award a mark for simply re-stating this, a valid explanation must be given.

Syllabus sections