# Physics P1 6.4 The expanding universe.

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What is light from distant galaxies?
Red-shifted.
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What does red-shift provide?
Evidence that the universe is expanding.
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If a wave source is moving relative to an observer, what happens to the wavelength and frequency of the waves detected by the observer and what is this called?
They will have changed (shifted) from the original proceeded by the source, this is called the Doppler effect.
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When the wave source moves away from the observer, what happens to the observed wavelength and frequency?
The wavelength increases and the frequency decreases.
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When the wave source moves towards the observer, what happens to the observed wavelength and frequency?
The observed wavelength decreases and the frequency increases.
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How can the Doppler effect be demonstrated?
With sound waves, for example an ambulance siren will sound different depending on whether it is moving away from you (pitch is lower) or towards you (pitch is higher).
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What are galaxies?
Large collections of stars.
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What has happened to light observed from distant galaxies?
It has be 'shifted' towards the red end of the spectrum. This is know as red-shift.
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What happens to wavelength and frequency as a result of red-shift?
Wavelength is increased and frequency is decreased.
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What would indicate that a galaxy is moving towards us?
Blue-shift.
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How are we able to see the effects of red-shift and blue-shift?
By observing dark lines in the spectra from galaxies.
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What happens the further away a galaxy is?
The bigger the red-shift.
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The bigger the red-shift, the further away the galaxy. What does this suggest?
That distant galaxies are moving away from us, and the most distant galaxies are moving the fastest. This is true of galaxies no matter which direction you look.
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All the distant galaxies are moving away from each other, what does this indicate?
The whole universe is expanding.
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What happens to the wavelength if a wave source is moving away from you?
The observed wavelength increases.
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Which galaxies are moving fastest?
The most distant ones.
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How does red-shift show that the universe is expanding?
The furthest galaxies are moving the fastest so everything is expanding outwards.
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**REMEMBER THAT LIGHT IS SHIFED TOWARDS THE RED END OF THE SPECTRUM- IT IS IMPORTANT TO REALISE THIS DOES NOT MEAN IT IS TURNED INTO RED LIGHT**
**LOOK UP LIGHT SOURCE AND PATTERN OF ABSORPTION LINES SHIFTED TO RED END OF SPECTRUM.
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## Other cards in this set

### Card 2

#### Front

What does red-shift provide?

#### Back

Evidence that the universe is expanding.

### Card 3

#### Front

If a wave source is moving relative to an observer, what happens to the wavelength and frequency of the waves detected by the observer and what is this called?

### Card 4

#### Front

When the wave source moves away from the observer, what happens to the observed wavelength and frequency?

### Card 5

#### Front

When the wave source moves towards the observer, what happens to the observed wavelength and frequency?