Convex and concave lenses
A lens is bound by two surfaces, at least one spherical.
A magnifying glass
A watchmaker looks at tiny parts through a small magnifying glass. If you touch it, you find its surface is curved, not flat. It is thicker in the middle than at the edges.
What do you think a lens that is thicker in the middle does to rays of light?
What this lesson covers
The idea
A lens is a transparent material bound by two surfaces, at least one spherical; a convex lens is thicker at the middle and converges light rays, while a concave lens is thicker at the edges and diverges them.
A magnifying glass
A watchmaker looks at tiny parts through a small magnifying glass. If you touch it, you find its surface is curved, not flat. It is thicker in the middle than at the edges.
What do you think a lens that is thicker in the middle does to rays of light?
- It brings them together
- It spreads them apart
- It lets them pass without changing
Three lenses
Look at the shape of each lens and at what it does to the parallel red rays. Open every tab.
Shape decides
The thick-middle lens pulled the rays together and the thick-edge lens pushed them apart.
A lens is a transparent material bound by two surfaces, of which at least one is spherical. A convex lens is thicker at the middle than at the edges and converges light rays. A concave lens is thicker at the edges and diverges them.
Notes
A lens has two surfaces, at least one spherical. A convex lens is thicker at the middle and converges light. A concave lens is thicker at the edges and diverges it.
Check yourself
A convex lens is
Which lens diverges light rays?
What must be true of the two surfaces of a lens?
A convex lens is also called a
- thicker at the edges than at the middle. That describes a concave lens.
- thicker at the middle than at the edges — correct. Yes!
- equally thick everywhere. A convex lens is thicker in the middle than at its edges.
- A convex lens. A convex lens converges light rays. It is also called a converging lens.
- Both lenses diverge rays. A convex lens converges rays, and a concave lens diverges them.
- A concave lens — correct. Yes!
- At least one of them must be spherical — correct. Yes!
- Both must be plane. Two plane surfaces would not make a lens. At least one surface must be spherical.
- Both must be spherical. At least one surface is spherical, and the other may be plane.
- diverging lens. A diverging lens is a concave lens.
- converging lens — correct. Yes!
- plane lens. A convex lens has curved surfaces. It is called a converging lens because it converges light.