Unit 5 in four lessons

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Unit 5 in four lessons
Light
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Refraction
Refraction happens when light moves from one
medium to another (example from air to glass)
OUT ? AWAY
Wave slows down Bends towards the normal
line Wavelength decreases
Wave speeds up Bends away from the normal
line Wavelength increases
IN ? TOWARDS
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Dispersion
Different colours have different wave speeds
through prism They have a different refractive
index So they refract by different amounts Red
refracts least, red refracts most (Violet is the
biggest bender)
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Three Refraction formulae (ITS JUST PUTTING IN
THE NUMBERS)
1 REFRACTIVE INDEX How much the speed changes
Speed in light in a vacuum Speed of light in
medium
Refractive index, n

2 SNELLS LAW How to calculate the
refractive index
Sin i
n
Sin r
Angle of incidence, i
Angle of refraction
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3 The critical angle Total internal
reflection)
Less dense fibres
More dense fibres
TIR only happens when light travels from a more
dense material to a less dense material the
angle is greater than the critical angle
c the critical angle nr index of material
light has entered n I index of material light
has come from
Sin c nr
ni
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Convex lenses (converging lenses)
Parallel rays are brought together
The thicker the lens the more the rays are bent
Diverging rays are made parallel
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Uses

1. Magnifying glass projectors to make images
   larger
2. Camera to focus the image on the film / sensor

When magnifying Magnification image size
object size
Lenses are moved forwards and backwards to focus
an image
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Finding the position size of an image
3 Draw a line from the centre through the focal
point
2 Draw a line across to the centre of the lens
Image is where they meet
Object
Focal point
1. Draw a line from the top of the object through
the middle of the lens
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e.g. Cameras
e.g.Projectors
e.g. Magnifying lens