# Diffraction

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• Created by: Emily
• Created on: 26-03-13 14:07
What is meant by Diffraction?
The spreading of waves when they meet obstacles, such as the edges of a slit.
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Where does the wave's energy travel?
Into the geometrical shadows of the obstacles.
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What happens to the waves if we increase the slit? Why?
The bigger the slit compared to the length of the wave, the less the wave diffracts, this is because more wavelengths can fit through the slit at once.
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Why can you hear someone through an open door even if you can't see them?
The typical wavelength for sound is 1m which is roughly the same width as a door frame, because of this the wave diffracts a lot around the door frame enable someone in another room to hear you.
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Does sound travel faster in water or air?
Sound travels 4.3 times faster in water than air.
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What happens to the frequency when a wave changes medium?
It stays the same.
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What equation can we use to find the frequency?
f = v1/λ1 = v2/λ2
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State the Principle of Superposition.
When waves travelling from two (or more) sources travel through the same region the resultant displacement is the vector sum of the displacement of the individual waves.
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What is constructive interference?
Where the amplitude is at its highest, the waves from the slits are arriving in phase and interfering constructively.
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What is destructive interference?
Where the amplitude is at its lowest, the waves are arriving in anti-phase and interfering destructively.
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What is monochromatic light?
Continuous oscillations of almost a single frequency.
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What is coherent light?
Monochromatic light with wave fronts continuous across the beam.
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What is meant by coherent sources?
Wave sources which have a constant phase difference and therefore must have the same frequency,
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What is a Diffraction grating?
A flat plate which is opaque except for thousands of straight parallel, equally spaced slits.
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Why is a Diffraction grating more accurate than Young's double slit experiment?
The fringes are not share: bright fringes gradually fade into dark. The bright fringes are therefore not very bright. The fringe separation is small.
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What equation can we use to find the wavelength of the light from a diffraction grating?
nλ = d sin θ
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If we used incoherent sources why wouldn't there be any fringes produced?
There'd be no constant phase relationship.
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## Other cards in this set

### Card 2

#### Front

Where does the wave's energy travel?

#### Back

Into the geometrical shadows of the obstacles.

### Card 3

#### Front

What happens to the waves if we increase the slit? Why?

### Card 4

#### Front

Why can you hear someone through an open door even if you can't see them?

### Card 5

#### Front

Does sound travel faster in water or air?