How do lenses work?

What the Activity is for

Explaining lenses.

This activity shows how knowing what happens as light refracts allows an understanding of lenses.

What to Prepare

• a means of sharing a large view of a computer screen
• the interactive presentation (see below)

What Happens During this Activity

Run through the interactive, with a commentary that emphasises using what is already known.

So draw on the refraction at each surface, emphasising the bending towards the normal as the light goes from a fast to a slow medium.

Also emphasise the bending away from the normal as the light changes from a slow to a fast medium. The rest of lens design is about arranging the angles between the two normals, so that you get the right amount of bending.

Here we show only convex lenses. Use the animation to show how these are made out of slices of prisms of glass of increasing steepness as you get towards the centre of the lens.