Light_presentation

2. Light
In this unit:
3) Properties of light
4) Reflection
5) Colours
6) Refraction

3. Part 1 – Properties of Light
Light travels in straight lines:
Las e r

4. Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.

5. Light travels much faster than sound. For example:
2) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.

6. We see things because they
reflect light into our eyes:
Homework

7. Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects Reflectors

8. Shadows
Shadows are places where light is “blocked”:
Rays of light

9. Properties of Light summary
• Light travels in straight lines
• Light travels much faster than sound
• We see things because they reflect light
into our eyes
• Shadows are formed when light is blocked
by an object

10. Part 2 - Reflection
Reflection from a mirror:
Normal
Incident ray Reflected ray
Angle of Angle of
incidence reflection
Mirror

11. The Law of Reflection
Angle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The
same !!!

12. Clear vs. Diffuse Reflection
Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions

13. Using mirrors
Two examples:
2) A car headlight
1) A periscope

14. Colour
White light is not a single colour; it is made
up of a mixture of the seven colours of the
rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is “split up”
by raindrops.

15. The colours of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet

16. Refraction
Refraction is when waves ____ __ or slow down due to
travelling in a different _________. A medium is
something that waves will travel through. When a pen is
placed in water it looks like this:
In this case the light rays are slowed down by the water
and are _____, causing the pen to look odd. The two
mediums in this example are ______ and _______.
Words – speed up, water, air, bent

17. Adding colours
White light can be split up to make separate colours.
These colours can be added together again.
Adding blue and red Adding blue and
makes magenta green makes cyan
(purple) (light blue)
Adding red Adding all
and green three makes
makes yellow white again

18. Seeing colour
The colour an object appears depends on the colours
of light it reflects.
For example, a red book only reflects red light:
White Only red light
light is reflected

19. A pair of purple trousers would reflect purple light
(and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light

20. Using coloured light
If we look at a coloured object in coloured
light we see something different. For
example, consider a football kit:
Shirt looks red
White
light
Shorts look blue

21. In different colours of light this kit would look different:
Red
Shirt looks red
light
Shorts look black
Shirt looks black
Blue
light
Shorts look blue

22. Some further examples:
Colour object
Object Colour of light
seems to be
Red Red
Red socks Blue Black
Green Black
Red Black
Blue teddy Blue
Green
Red
Green camel Blue
Green
Red
Magenta book Blue
Green