Eyes

D. Crowley, 2008

Eyes

To know how our eyes are developed to allow us to see the world around us

Shadows

In a theatre a clown is performing. A powerful spotlight shines onto the stage, creating a black shadow behind the clown that the audience can see…

What is the light source?

Explain how the shadow behind the clown is formed…

Explain how light rays from the spotlight reach the audience, so that they can see the clown…

Shadows

The light source is the spotlight

Light shines from the spotlight. The ray of light cannot pass through the clown (who acts as a barrier). As light travels in straight lines it cannot bend behind the clown, so a shadow forms where no light reaches

(1) What is the light source; (2) Explain how the shadow behind the clown is formed; (3) Explain how light rays from the spotlight reach the audience, so that they can see the clown

Light rays reach the clown, and reflect from him. These rays enter the eyes of the people in the audience, so they see him!

The Eye We see objects because light reflected from them enters our

eyes

The light from luminous objects such as stars and lamps may enter our eyes directly

Objects which do not make their own light are non-luminous, but we can still see them if light from a luminous object reflects or scatters off them into our eyes

A ray diagram, showing a luminous object (bulb) and non-luminous

object (battery)

The EyeCopy a diagram of the eye, and label the main parts

The Eye

Retina - the light-sensitive part of the eye, covered in light receptors called rods and cones

Optic nerve - carries impulses from the light receptors to the brain

Lens - focuses light onto the retina

Pupil - the hole in the iris where light passes through

The Eye

Suspensory ligaments - control the shape of the lens, along with the ciliary muscle

Ciliary muscle - controls the shape of the lens, along with the suspensory ligaments

Cornea - refracts (bends) light into the eye

Iris - changes the shape of the pupil to control how much light enters the eye

Pinhole Camera

Cameras work in similar ways to eyes. The simplest kind of camera if a pinhole camera

It does not have any lenses, but a small hole made with a pin lets light in, which forms an image on the back of the screen

The hole at the front can be made bigger or smaller, controlling the amount of light which gets in

Your eyes work like this too, where the pupil gets smaller or bigger depending upon the amount of light