7th Grade Science Student ebook

4.3 Light and Living Things.

CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONS

Lenses

A lens and its

optical axis

A lens is an object that is designed to refract light in a specific way.

Many devices you use contain lenses (Figure 4.16). All lenses have

an imaginary line that goes through the center called an axis.

While there are different kinds of lenses, light traveling along the

axis of any lens is not bent. There are two basic kinds of lenses;

convex and concave.

Convex lenses Light rays that enter a convex lens parallel to its axis refract and

meet at a point called the focal point. The distance from the center

of the lens to the focal point is the focal length. Convex lenses are

sometimes called converging lenses.

Concave lenses Light rays that enter a concave lens parallel to its axis refract and

spread out, diverging (moving apart from each other) as they exit

the lens. The focal point of a concave lens is located on the same

side of the lens as the light source. Imaginary lines are drawn

backward in the opposite direction of the diverging rays. The focal

point is where the imaginary lines meet. The distance from the

focal point to the center of the lens is its focal length. Concave

lenses are sometimes called diverging lenses.

Figure 4.16: Some devices that use

lenses.

lens - an object designed to

refract light in a specific way.

focal point - a point where light

rays meet.

focal length - the distance from

the center of the lens to the focal

point.