| A | B |
|---|
| concave lens | A lens that is thicker at the edges than in the middle. |
| convex lens | A lens that is thicker in the middle than at the edges. |
| focal length | The distance along the optical axis from the center of the mirror to the focal point. |
| focal point | The point at which light rays pass through on the optical axis. |
| law of reflection | The angle of incidence is equal to the angle of reflection. |
| lens | A transparent object with at least one curved side that causes light to bend. |
| light ray | A narrow beam of light that travels in a stright line. |
| medium | The material through which a wave travels. |
| refracting telescope | Two convex lenses that forms an image of a distant object. |
| reflecting telescope | A concave mirror that gathers the light from distant objects. |
