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Light Revision Notes

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Light Revision Notes

When waves meet a boundary, where the medium (stuff) changes, they

may:

* reflect- bounce back e.g. light at a mirror, sound echoing off a

wall

* refract- go through the boundary, usually changing speed and

direction as they do e.g. light through spectacles, water waves

going from deep to shallow water

* get absorbed - give up their energy, warming up the surface layer

e.g. in a solar heater

Quite often, there's some of each happening.

High tier only

* When waves meet a gap, they carry on, but diffract - they spread

out into the shadow behind the gap.

* The extent of diffraction (spreading) depends on the width of the

gap.

1. a gap similar to the wavelength: a lot of spreading, no sharp

shadow e.g. sound through a doorway

2. a gap much larger than the wavelength: little spread, sharp shadow

e.g. light through a doorway

Reflection

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When waves reflect, they always do it regularly.

Remember:

i = r

(The angle of incidence = the angle of reflection)

Rough surfaces

Each bit of the surface obeys this law, but the overall effect of the

jagged surface is to scatter the light diffusely.

The reflected waves head off in all directions, e.g. sunlight on a

piece of paper.

Smooth surfaces

These act as mirrors. The rays are reflected uniformly and can form

images. They can:

1. be focused to a point e.g. sunlight off a concave mirror telescope

2. appear to come from a point behind the mirror e.g. a looking glass

Refraction

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If a surface is transparentto waves, some or most of the waves hitting

the surface will pass through. The rest get internally reflected.

The speed of waves usually changes when they cross a
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