Lenses
Some lenses are thick in the middle. Some are thin. Light passes through them in different ways.
Step 1 of 4
- Two parallel rays reach the glass.
- Each ray bends at the first curved face.
- Each ray bends again at the second face.
- Thicker in the middle: the rays meet.
The rule
A lens is a curved piece of glass or plastic. A convex lens is thicker in the middle. A concave lens is thicker at the edges.
A lens thicker in the middle (convex) makes parallel rays meet. A lens thinner in the middle (concave) makes them spread. A flat glass sheet does not make them meet or spread.
Spectacles, or glasses, and phone cameras use lenses. The eye has a lens too.
Watch out!
A wet drop on a leaf can act as a lens. Never use a drop, or any lens, to look at the Sun.
Slide the shape. Watch five parallel rays.
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