The New Childrens Encyclopedia

LIGHT FANTASTIC

241

SCIENCE

REFRACTION When light

crosses the boundary between

two media with different

densities (such as air and water),

it bends, or “refracts”. This is why

objects standing in water appear

distorted at the surface. If you try to

touch a coin or pebble in a bucket of

water, it will not be exactly where

your eyes tell you it is.

Heat haze

Refraction can happen when

light passes through air of

mixed density. Cool air over

hot ground contains layers of

variable density, and light

passing through the layers is

bent, causing a shimmering

heat haze. In extreme cases the

effect results in a “mirage” – a

watery-looking reflection of

the sky.

Lenses A lens is a transparent

object with curved surfaces that

refract light in a predictable way.

An object close behind a bulging

or “convex” lens will appear

magnified while one seen

through a dished or “concave”

lens will appear reduced in size.

Telescopes, microscopes, and

spectacles all use lenses.

 SHORT SIGHT is

when the eye focuses an

image too far forward.

It is corrected with a

concave lens.

 LONG SIGHT

causes the image to

focus too far back, so

the retina only detects

a blur. It is fixed with

a convex lens.

REFLECTION When light strikes an

object, some of it is bounced back or

“reflected”. The angle of reflection is

always the same as the angle at which

the light hits the surface, so on a smooth

surface we see a perfect reflection, or

mirror image. If the surface is curved or

uneven, the image is distorted.

The break in the

straws is an

illusion caused

by refraction.

Concave lens

 IMPERFECT eyesight can be

corrected with artificial lenses.

FIREWORKS

The atoms of different

materials emit light of

different colors or

wavelengths. Firework

makers use this to create

wonderful displays.

Convex lens