Lenses
Science: KS3, topic 3.3.25
Lenses
Lenses are transparent. All light needs to be focused to form an image.
Convex lenses
- A convex lens is like the lens in your eye.
- The lens is called a converging lens.
- The lens is larger in the middle than on the top and bottom.
- The lens focuses light at the focal point.
Uses of convex lenses
- Glasses with convex lenses are used to aid people who are long sighted.
- Convex lenses are also used in magnifying glasses and cameras.
Concave lenses
- A concave lens is also called a diverging lens.
- A concave lens is thinner in the middle and slightly bigger on top and bottom.
- Glasses with concave lenses help people who are short sighted.
Refraction
Light waves pass through different mediums. So light waves change speed. Light waves refract at the boundary between air and plastic.
Refraction
- Light travels between two different mediums.
- So light will refract.
- Air, plastic and glass are different mediums.
Slowing down
- As light enters glass or plastic, light will slow down.
- So light will change direction.
- As light slows down, light bends towards the normal.
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Uses of refraction
- As light enters the eye, the cornea and the lens refract light.
- So an image will form on the retina.
Spectrum of colours
- A prism will refract light to form a spectrum of colours.
- Forming a spectrum of colours is called dispersion.
Archer fish
- The archer fish spits water at its prey.
- The archer fish accounts for refraction at the boundary between air and water.
Test yourself on Lenses
Which statement about each lens is correct?
Which kind of lens is found in your eye?
A student is short-sighted. What type of lens will help them see clearly?
What happens to light rays passing through a lens that is thicker in the middle than at the edges?
What does the term 'dispersion' refer to?