Light – Part 2Seeing

Year 7 Science

Front View of the Eye

Parts of the eye for protecting eyeball

• Eyelids are skin flaps on the outside of your eyes. They are used to protect the eyeball from dust, smoke, bright light or physical injury.

• Tear Glands are used to provide liquid that helps lubricate the eye. The lubricant is also important for washing away small particles of dust that may irritate the eye.

• The small hole in the inside corner of the eye is the opening of the tear duct. The tear ducts drain any excess liquid produced by the tear glands.

Front View of the Eye

Cross section view of eye

Parts of the eye used in vision• The Cornea is a clear thin ‘skin’ that covers

the front of the eye and allows light to pass into the eyeball. The cornea is curved so that light is ‘bent’ or refracted towards the pupil.

Refraction• The ‘bending’ of light is called Refraction. It

happens when light travels between substances of different densities – like air to water. Try this experiment at home to see how refraction happens..

Parts of the eye used in vision• The coloured part in front of the eye is called the iris.

This is a ring of muscle which changes in size, depending on the light intensity – just like the ‘aperture’ in a camera lens.

• When we say someone has brown or blue eyes we are referring to the colour of the iris.

Parts of the eye used in vision• The dark central area is the pupil and is

actually an opening in the iris through which light passes. It is large when there is little light and small when there is plenty of light.

Parts of the eye used in vision• As light rays continue to pass through the eye, they are

refracted a little more by the lens in the eye.• The lens is clear and jelly-like and is connected to muscles

which can make it thick or thin. • The lens bends light to focus it on the retina at the back of the

eyeball. The retina is sensitive to both the colour of light and brightness of light.

What do lenses do ?• The lens in your eye bends light in order to focus it on

the retina. The drawing below shows how light rays are bent with a lens:

• Notice how the lens bends light rays so they come to a point. We call this point the focal point or focus.

Types of lenses• Lenses can be either converging or diverging.

Your eye uses a converging lens.

How the eye focuses

Sending image signals to the brain• Although your eye receives the light and produces an

image of what you see, it is your brain that interprets and makes sense of the image.

• The receptors on the retina respond by sending signals to the optic nerve which in turn sends signals to the brain.

Summary

Homework:

• Read pages 188-189 of Core Science 1 text and answer all Remember and Think Activities on page 189.

Short-sightedness

Long-sightedness