# AQA P1.5 Sound and the universe

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• Created by: Rchilds
• Created on: 16-05-17 12:40
What is a sound wave?
A longitudinal wave that transfers energy by oscillating particles (colliding with each other and passing the energy along)
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Why is sound fastest in solids?
The particles are closer together so collide more often
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What determines the pitch of a sound wave?
The frequency. High frequency = high pitch, low frequency = low pitch
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What determines the volume of a sound wave?
The amplitude. Large amplitude = loud sound
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What is the reflection of a sound wave called?
An echo
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What is the Doppler effect? (note: this can happen with any wave e.g. sound, light, microwaves)
If a sound wave source is moving relative to an observer there will be a change in the observed wavelength and frequency. (speed doesn't change as that depends on the material it is travelling through)
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What happens to the sound wave if the source is moving towards the observer?
It's frequency increases/wavelength decreases so it's pitch is higher
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What happens to the sound wave if the source is moving away from the observer?
It's frequency decreases/wavelength increases so it's pitch is lower
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What is the Doppler effect in light called?
Red shift or blue shift
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What is the order of the colours in the rainbow spectrum, which has the highest frequency and shortest wavelength?
Red, Orange, Yellow, Green, Blue, Indigo, Violet. Violet has the highest frequency and shortest wavelength
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What do we see when we look at light from galaxies?
We see the rainbow spectrum with black lines running through it. These are absorption lines from chemicals in the star (H and He). We know where the pattern of lines should be, but they are redshifted
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What is red shift?
When observing light from distant galaxies, the light is shifted towards the red end of the spectrum. This means it has a LOWER frequency so the galaxy must be moving away from us
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What is blue shift?
The opposite of red shift. It happens when stars (or very rarely galaxies) are moving towards us so the frequency is INCREASED and the light is shifted towards the blue end of the spectrum.
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Where do we see red-shift?
All distant galaxies (and any stars in our own galaxy that are moving away from us)
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Where might you see blue shift?
Light from stars in our own galaxy moving towards us, or light from a star that is orbiting another star (but only when it is moving towards us)
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How can you tell how fast a galaxy is moving away from us?
The faster it is moving, the more red shifted it will be
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What is the pattern seen between how far away a galaxy is from us and how fast it is moving?
Galaxies that are further away are moving faster (so their light is more red-shifted)
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What is red shift evidence for?
That the universe is expanding so it supports the Big Bang Theory
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What is your model answer to explain how redshift tells us the universe is expanding?
Light from distant galaxies is redshifted, this tells us they are all moving away from us. Light from the furthest galaxies is redshifted the most so are moving the fastest. The explanation for this is that the universe itself is expanding
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What is the Big Bang Theory?
Before time began, the universe was all compacted into a single point (a singularity). It then started to expand, time began and gradually particles (then stars - planets - galaxies etc) were formed. The universe is still expanding
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Why is big bang theory the most popular theory at the moment?
It has the most evidence (Redshift and CMBR). Currently, no other theories can explain where CMBR came from.
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What is CMBR?
Cosmic Microwave Background Radiation. When you look into space using a microwave telescope, there are microwaves (electromagnetic radiation) everywhere. This is thought to be left over energy/radiation from the big bang
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## Other cards in this set

### Card 2

#### Front

Why is sound fastest in solids?

#### Back

The particles are closer together so collide more often

### Card 3

#### Front

What determines the pitch of a sound wave?

### Card 4

#### Front

What determines the volume of a sound wave?

### Card 5

#### Front

What is the reflection of a sound wave called?