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Block 2 Unit 3Page 1

Science

Grade 4Unit 3

What can we see?

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Block 2 Unit 3Page 2

What can we see?

The Sun, fires and lamps are all sources of light. Mirrors and otherobjects reflect light. They do not make their own light.

Sources of light

A source of light makes light. The Sun and other stars, fires, torches andlamps all make their own light and so are examples of sources of light.When a television is turned on, it produces light.

Remember! You must never look directly at the Sun. It is so bright that itcan damage your eyes very quickly.Some animals, such as fireflies and glow-worms, are light sources. Theymake their own light to attract mates.

Glow worm firefly

Reflection

A mirror is not a source of light. It doesn't make its own light, it justreflects light.The moon is not a source of light. It reflects light from the Sun.You would not be able to see a reflector of light, such as a mirror, in a

completely dark room.

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Block 2 Unit 3Page 3

Opacity

What happens when light hits an object?Three things can happen:1) Light passes through easily if the object is transparent .

2) Light passes partially, the material passes some light if the object is

translucent .

3) Light is blocked; doesn’t pass at all if the object is opaque .

Notes:Opaque materials make a clear shadow because they block light.

e.g.: wood

Transparent materials make a faint shadow.Some materials look shiny because they reflect light well.

e.g.: metal

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Block 2 Unit 3Page 4

How we see things

Light travels in straight lines. When light hits an object, it is reflected(bounces off) and enters our eyes. This is how we see the object.

When light from an object is reflected by a surface, it changes direction.It bounces off the surface at the same angle as it hits it.

Smooth, shiny surfaces such as mirrors and polished metals reflect lightwell.

Dull and dark surfaces such as dark fabrics do not reflect light well.

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Block 2 Unit 3Page 5

Parts of the eyeYou can check out different parts of the eye by looking at your own eyein the mirror or by looking at a friend's eye.

Some of the eye parts are easy to see, while other parts are hiddeninside the body.

The eye is about as big as a ping-pong ball and sits in a little hollow area(the eye socket) in the skull.

A- Outer parts:

1- Iris : It is the colorful part of the eye, When we say a person has blueeyes, we really mean the person has blue irises!

Humans have different eye colors like: Brown, Hazel, green and blue.

2 - Pupil: The pupil is the black circle in the center of the iris, which isreally an opening in the iris, and it lets light enter the eye.To see how this works, use a small flashlight to see how your eyesrespond to changes in brightness. The pupils will get smaller when thelight shines near them and they'll open wider when the light is gone.

3- Sclera : The sclera covers most of the eyeball.Look very closely at the white of the eye, and you'll see lines that looklike tiny pink threads. These are blood vessels, the tiny tubes that deliverblood, to the sclera.

4 - Tear duct: Every time you blink your eye, a tiny bit of tear fluidcomes out of your upper eyelid. It helps wash away germs, dust, or other

particles that don't belong in your eye.

Tear duct

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Block 2 Unit 3Page 6

B- Inner Parts:

1- Lens: After light enters the pupil, it hits the lens. The lens sits behindthe iris and is clear and colorless. The lens' job is to focus light rays on

the back of the eyeball.

2- Optic nerve : it is the great messenger in the back of your eye.

The optic nerve carries the messages from the eye to the brain to read

these messages and make you see the different pictures.