• Light is needed before we can see anything (See reflections)
  • Light is given out from a luminous source eg the Sun or a projector lamp.

Remember that it is dangerous to look straight at the Sun because the light is too bright.
If you wish to look towards the Sun (eg during a Solar Eclipse) then it is very important that you look through a special dark filter (sun glasses are NOT dark enough)

luminous

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

 


Reflections

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

Reflection

Reflection. Notice the direction of the arrows.

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

Reflection

Reflection from a mirror

 

Using reflection 1

Periscope 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

ks2_light_clip_image001_0008 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

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

shadow1

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

shadow2

 

If the ball moves towards the screen the shadow will get Larger or smaller?

If the ball moves nearer to the light the shadow will get Larger or smaller?

Quick test

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

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

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

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

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

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