Light

 

Light is given out from a luminous source eg the Sun or a projector lamp.

 

Luminous sources in a room

Light bulb

Candle

TV set

Window

Table lamp

Remember:
The Moon does NOT give out light
We see the moon because light from the sun is reflected from the Moon towards the Earth.

 

 

Light travels in straight lines which can be drawn as a straight line with an arrow in the middle.

 

  • Something that we can see through is called transparent
  • Something that blocks light is called opaque
  • Something we can see shapes through but not any detail (like a shower curtain) is called translucent

In order to see anything light has to be reflected off of it and enter our eye.

 

 

Reflections

Rays of light will reflect of a smooth surface like a mirror.

When they do the angle that they leave the mirror will be the same as the angle that they hit the mirror

 

Using reflection 1

A periscope

A periscope is a tube containing two mirrors.

It lets you look over a wall or around corners.

This is a diagram of someone looking at a boat using a periscope.
It shows the path taken by the light as it travels from the ship to the person's eye.

 

Using reflection 2

This is the diagram of a boy's bedroom.

The desk part of the room is separated from the bed by a screen.

 

Mum is making sure that the boy is doing his homework properly but the boy is still managing to watch TV by looking in the mirror!

 

The red lines show the path of the light as it travels from the TV to the boy

 

Shadows

Shadows are formed when rays of light are blocked and prevented from reaching the surface

Shadows

A stick forms a shadow because it blocks the light
 shadow

An opaque object (like a stick) forms the best shadow

A translucent object forms a slight shadow

A transparent object may not form any shadow

 

Investigating the size of a shadow

 

In this diagram light is shining on a white screen.

An orange ball is blocking the light, forming a shadow on the screen.

 

This experiment shows us that light travels in straight lines.

In the experiment above there are three things we can change:

We can move the ball towards the screen
(which will change distances A and B)

We can move the light towards the ball
(which will change distances A and C)

or we can move the screen towards the ball
(which will change distances B and C)

 

It is important that we change only one of these at a time or it will not be a fair test

 

If the ball moves towards the screen the shadow will get

If the ball moves nearer to the light the shadow will get

 

 

Quick test

Name the main source of light we use to see things outside ?

If a light bulb is moved nearer to an object, the shadow from the object would get larger or smaller ?

The Moon is a luminous object and gives out light. True or False?

A solid object that blocks out light is transparent, translucent or opaque?

Complete this sentence: Light always travels in ..............

When light is blocked it formes a ............................ ?

 

 

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