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If a police car is travelling away from an observer and its siren is on, the wavelength of the siren will be longer than when the car is moving towards the observer.

# Waves - The Doppler Effect and Redshift

This GCSE Physics quiz about waves will challenge you on the Doppler effect and redshift. The Doppler effect is also known as the Doppler shift. It describes the change in the wavelength of a wave that is being emitted by a moving object. The idea was first suggested in 1842 by the Austrian scientist Christian Doppler. He knew that a ship meets waves at a faster rate (higher frequency) when it is sailing in the direction from which the waves are coming than if it was sailing in the same direction that the waves were travelling. He knew that both sound and light were waves so he reasoned that the same effect would be noticed. He also said that it didn't matter whether it was the source of the waves that was moving or the person observing them.

Evidence to support the Doppler effect came a few years later. A Dutch scientist (with the incredibly long name of Christophorus Henricus Diedericus Buys Ballot) used musicians and a train to test the idea.

1.
If a police car is travelling away from an observer and its siren is on, how will the wavelength be different to when the car is moving towards the observer?
Shorter
Longer
The same
Impossible to tell
Successive waves will arrive later than they would if the car was stationary
2.
How does the frequency and wavelength of a wave source change when it moves towards an observer?
The wavelength increases whilst the frequency decreases
The wavelength decreases whilst the frequency increases
The wavelength increases and the frequency increases
The wavelength decreases and the frequency decreases
If the wavelength of a particular wave decreases, then the frequency will always increase as more waves will pass the observer each second
3.
How does the frequency and wavelength of a wave source change when it moves away from an observer?
The wavelength decreases whilst the frequency increases
The wavelength increases whilst the frequency decreases
The wavelength decreases and the frequency decreases
The wavelength increases and the frequency increases
For light, the effect is only noticeable when the movement is at extremely high speeds
4.
It can be observed that there is an increase in the wavelength of light received from distant galaxies. The further away the galaxy is, the faster it is moving away from us and the larger the observed increase in wavelength. What is this effect commonly known as?
Redshift
Blueshift
Whiteshift
Purpleshift
It is known as redshift as the wavelengths of light received from objects travelling away from us are displaced towards the red end of the electromagnetic spectrum. Similarly, light-emitting objects travelling towards us have wavelengths which are shifted towards the blue end of the spectrum and thus this effect is known as blueshift
5.
Where does C.M.B.R come from?
Radiation present shortly after the beginning of the Universe
Radiation generated by humans on Earth
Radiation generated by gas giants such as Jupiter and Saturn
It has a temperature close to absolute zero
6.
What is the Doppler effect?
The Doppler effect is the change in the observed wavelength and frequency of a source which is stationary relative to an observer
The Doppler effect is the change in the observed wavelength and frequency of a source which is moving relative to an observer
The Doppler effect is the change only in the observed wavelength of a source which is stationary relative to an observer
The Doppler effect is the change only in the observed frequency of a source which is stationary relative to an observer
Both the frequency and the wavelength change when a source is moving relative to an observer. You can hear this effect yourself by listening carefully to traffic going past on a main road. You can hear how the sound changes when the vehicles are travelling towards you and away from you
7.
If a police car is travelling towards an observer and its siren is on, will the frequency of the siren be higher, lower or the same as when the car is moving away from the observer?
Lower
Higher
The same
Impossible to tell
Successive waves will arrive sooner than if the car was stationary
8.
Which is the only current theory that explains and accounts for the existence of the C.M.B.R?
Theory of Special Relativity
General Theory of Relativity
Little Bang Theory
Big Bang Theory
This has become the accepted theory of the origin of our Universe but there are still many unanswered questions
9.
Why does redshift support the idea of the Big Bang theory?
It demonstrates that the Universe is expanding as more distant galaxies are moving away from us
It demonstrates that the Universe is collapsing as more distant galaxies are moving towards us
It does not offer any insight as to whether the theory is true or not
It shows that the Universe in stationary and not expanding or shrinking
The further away the galaxies are, the faster they appear to be moving
10.
What is the cosmic microwave background radiation (C.M.B.R.)?
A form of sound wave which fills the whole of the Universe and is thought to be a remnant of the early stages of the Universe's life
A form of mechanical wave which fills the whole of the Universe and is thought to be a remnant of the early stages of the Universe's life
A form of electromagnetic radiation which fills the whole of the Universe and is thought to be a remnant of the early stages of the Universe's life
There is no such thing as the C.M.B.R
Scientists think that by studying the C.M.B.R, they can understand some of the conditions which existed in the early parts of our Universe's development