SECTIONS 11.7 AND 11.8

REFRACTION & LENSES

REFRACTIONWhat is Refraction?• when light passes from one material (aka medium) to

another, it bends because the speed of light travels at different speeds in different mediums

Ex. When light rays move from water into air, they speed up and bend away from the normal (that’s why a fish looks closer to the surface than it really is)

LIGHT TRAVELS THRU WATER

(why we see blue best)

• Light can undergo partial reflection and refraction at the same time at a surface. Ex. Sunglasses, two way mirrors (buildings = less air

conditioning)

REFRACTION - VOCABULARY

LENSES – USING REFRACTIONWhat is a Lens?• A lens is a curved, transparent device that

causes light to refract as it passes through• Like mirrors, can be convex or concave• Many optical devices use more than one lens

Ex. A microscope has objective and eyepiece lenses)

CONVEX LENSESWhat does a convex lens look like?

A convex lens is thicker in the middle than at the outside edge (bulges outward)

• Cause light rays to converge (come together) at a focal point • A ray passing straight through the centre of the lens (at a 90˚ angle) will not refract (bend)

CONVEX LENSES• Usually used to make objects look larger, so long

as you have the object close to the lens. Example. A magnifying glass

• Like concave mirrors, if the object is farther from the lens it will produce an inverted image that can either be larger or smaller depending on how far away it is.

CONCAVE LENSESWhat does a concave lens look like?

A concave lens is thinner in the middle than at the outside edge (caved inward)

• Cause light rays to diverge (spread apart)• Like convex lenses, rays passing through the centre will not refract

CONCAVE LENSES• Always produce a smaller, upright image of the

object• Not as common as convex lenses• Used in some types of eyeglasses (for

nearsightedness) and some telescopes

SUMMARY OF LENSES