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Refraction, lenses and colour
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Light bends when it passes into glass or water. White light is really a mixture of colours.
Refraction
Refraction is the bending of light as it passes from one material into another, because it changes speed.
Going from air into glass or water, light slows down and bends towards the normal. Coming out, it speeds up and bends away from the normal.
This is why a straw in a glass of water looks bent, and a pool looks shallower than it really is.
Going from air into glass or water, light slows down and bends towards the normal. Coming out, it speeds up and bends away from the normal.
This is why a straw in a glass of water looks bent, and a pool looks shallower than it really is.
Lenses
A convex lens is fatter in the middle. It bends light rays so they meet at a focal point.
Convex lenses are used in magnifying glasses, cameras and your eye.
The lens of the eye focuses light onto the retina, just as a camera lens focuses light onto a sensor.
Convex lenses are used in magnifying glasses, cameras and your eye.
The lens of the eye focuses light onto the retina, just as a camera lens focuses light onto a sensor.
Colour
White light is a mixture of colours, each with a different frequency. A prism splits it into a spectrum: red, orange, yellow, green, blue, indigo, violet (dispersion).
An object looks red because it reflects red light and absorbs the other colours. White objects reflect all colours; black objects absorb them all.
A filter lets through (transmits) only its own colour. A red filter transmits red and absorbs the rest.
An object looks red because it reflects red light and absorbs the other colours. White objects reflect all colours; black objects absorb them all.
A filter lets through (transmits) only its own colour. A red filter transmits red and absorbs the rest.
A blue shirt is seen in pure red light. What colour does it look, and why?
- A blue shirt reflects only blue light.
- There is no blue light to reflect.
- It absorbs the red light.
Answer: Black: it absorbs the red light and has no blue light to reflect.
Refraction is bending caused by a change of speed: into glass, light slows and bends towards the normal. Convex lenses focus light. White light is a mix of colours; objects reflect their own colour and absorb the rest; filters transmit their own colour.
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