Lenses

Lens- a transparent material with at least 1 curved surface that causes light rays to bend, or refract, as they pass through.

There are 2 types of lenses

1. Convex Lens

2. Concave Lens

• Convex lens- the lens is thicker in the middle than at the edges. Convex lens focuses the light rays at the focal point.

Focal Point

Focal Length

http://en.wikipedia.org/wiki/File:Large_convex_lens.jpg

• Concave lens- the lens is thinner in the middle than at the ends.

Concave lens refracts the light rays so they spread out.

http://en.wikipedia.org/wiki/File:Concave_lens.jpg

Lens Location Image Size

Convex -far away inverted -small

-close inverted -larger

-very close upright -larger

Concave

-anywhere upright -small

Uses of Lenses

• Farsightedness- when you can see distant objects clearly but can’t bring nearby objects into focus.

-The eyeball’s lens isn’t curved enough so you need a convex lens.

http://en.wikipedia.org/wiki/File:Hypermetropia.svg

• Nearsightedness- when you can see nearby objects clearly but can’t bring distant objects into focus.

-The eyeball’s lens isn’t flat enough so you need a concave lens.

• Refracting Telescope- uses 2 convex lenses to gather and focus light from distance objects.

• Reflecting Telescope- uses a concave mirror, a plane mirror and a convex lens to collect and focus light from distance objects.

• Microscope- uses 2 convex lenses with short focal lengths to magnify small objects.

Refracting Telescope

Reflecting Telescope

Microscope