Refraction and Lenses

7 SCIENCE

Review: What is refraction?

• Refraction occurs when light bends – Light bends as it passes from one

substance to another– Ex. A straw in a glass into

water

• Refraction can be caused by a lens• A lens is a transparent object with at least one

curved side that causes light to bend– More curved sides = more light bends

Lenses• Concave and convex lenses

form images OPPOSITE to that in concave and convex mirrors

• Convex lens– Thicker in the center than at

the edgesex: magnifying glass

• Concave lens– Thicker at the sides that in the

center ex: glasses for people that cannot see far objects

Convex lenses

• Light rays travelling through a convex lens are bent so they meet at a focal point

• Image formed is similar to that of a concave mirror– If the object is 2+ (or more) focal lengths from the lens,

the image appears inverted and smaller

– If the object is closer to the lens than one focal length, the image is upright and larger

Concave lenses

• Light rays travelling through a concave lens are bent and spread away from each other, do not meet

• Image formed is similar to thatof a convex mirror– Image formed is

upright and smaller than the object

– Ex: eyeglasses if you cannot see far

Which pictures show a concave lens? Convex lens? How do you know?