7 Lenses and Mirrors

Lenses

A lens is a piece of transparent material that is shaped so that it will refract light (or other waves) in a certain way.

Convex lenses (like the one shown here) bend light inwards - if you hold a convex lens close to an object then it appears much bigger than it really is. In this way, the lens is working like a magnifying glass.

A concave lens, on the other hand, is thinnest in the middle and thick at the outside: the opposite to a convex lens. They bend light in the opposite way is well - light is bent outwards.
If you look at something close up through a concave lens then it appears smaller than it really is.

a convex lens

Now answer these questions

  1. What does a lens do to light ?
  2. What lens is thin at the edge and thick in the middle ?
  3. In what way does a convex lens bend light ?
  4. What does an object look like through a convex lens ?
  5. What lens is thin in the middle and thick at the edge ?
  6. In what way does a concave lens bend light ?
  7. What does an object look like through a concave lens ?

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Curved Mirrors

In lesson 4 we saw that light bounces off a mirror at the same angle that it hits: the angle of incidence is equal to the angle of reflection.

For a curved mirror this is still true, but the situation is a little more complicated.
Like lenses, there are two different types of curved mirror. Mirrors that curve inwards are called concave (like the one shown here); and ones that curve outwards are convex.

A concave mirror will reflect light inwards to a point. These types of mirror can be used to make a solar furnace which focusses light from the Sun onto a single point: creating very high temperatures.

Convex mirrors reflect light outwards. These mirrors are often used in shops so that the shopkeeper has a good view of the whole of their shop.

a concave mirror

Now answer these questions

  1. What does a mirror do to light ?
  2. What mirror is curved outwards ?
  3. In what way does a convex mirror bend light ?
  4. Where can you use a convex mirror ?
  5. What mirror is curved inwards ?
  6. In what way does a concave mirror bend light ?
  7. Where can you use a concave mirror ?

You scored out of 7 on that test