Edexcel GCSE Physics 1PH0
Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves
Light and the Electromagnetic Spectrum
Radioactivity
Astronomy
Energy – Forces Doing Work
Forces and Their Effects
Electricity and Circuits
Static Electricity
Magnetism and the Motor Effect
Electromagnetic Induction
Particle Model
Astronomy
The Doppler effect and red-shift in galaxies
- 3 things to know
- Paper 1
Overview
How observed wavelength and frequency change for a source moving away or towards an observer, the ambulance siren, what red-shift is, and how it grows with a galaxy's distance and speed.
What you need to know
Answer each one before you reveal it.
Explain why the pitch of a siren on an ambulance seems to drop as the ambulance drives past a listener.
What happens to the observed wavelength of waves from a source that is moving away from an observer?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What happens to the observed wavelength of waves from a source that is moving away from an observer?
Model answer
The observed wavelength increases.
- 2
What happens to the observed frequency of waves from a source that is moving away from an observer?
Model answer
The observed frequency decreases.
- 3
What happens to the observed wavelength and frequency of waves from a source that is moving towards an observer?
Model answer
The observed wavelength decreases and the observed frequency increases.
- 4
Explain why the pitch of a siren on an ambulance seems to drop as the ambulance drives past a listener.
Model answer
While the ambulance approaches, the sound waves reach the listener at a higher frequency, and once it is moving away the frequency received is lower, so the pitch falls.
- 5
When a wave source moves relative to an observer, does the frequency emitted by the source itself change?
Model answer
No, the source emits the same frequency as before and only the frequency received by the observer is different.
- 6
State the condition needed for an observer to notice a change in the frequency of waves coming from a source.
Model answer
The source and the observer must be moving relative to one another.
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