Light ppt for bed

1. By VIKAS SHARMA

2. Light and Sound
In this unit:
1) Properties of light
2) Reflection
3) Colours
4) Refraction
5) Properties of sound
6) Hearing

3. Part 1 – Properties of Light
Light travels in straight lines:
Laser

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:
1) 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
Ex- Sun, Stars,
electric blub ,etc
Reflectors
Ex- Mirror, White
sheet, wall, etc

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

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

10. Part 2 - Reflection
Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of
incidence
Angle of
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. Regular vs. Diffuse Reflection
Smooth, shiny surfaces
have a regular reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions

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

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

17. 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
light
Only red light
is reflected

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

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

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

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

22. 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 ____ .
In this case the light rays are slowed down by the water
and is causing the pen to look odd. The two mediums in
this example are ______ and _______.
Words – speed up, medium, bent ,water, air,

23. Sound – The basics
We hear things when they vibrate.
If something vibrates with a high frequency (vibrates very
______) we say it has a _____ pitch.
If something vibrates with a low frequency (vibrates
______) we say it has a ____ pitch.
The lowest frequency I could hear was…
Words – slowly, low, high, quickly

24. Drawing sounds…
This sound wave has
a _____ frequency:
(high)
This sound wave has a
___ frequency:
(low)

25. Drawing sounds…
This sound wave has
a _____ amplitude.
(loud)
This sound wave has
a _____ amplitude.
(quiet)

26. Hearing problems
Our hearing range can be damaged by several
things:
1) Too much ear wax!
2) Damage to the auditory nerve
3) Illness or infections
4) Old age (not like Mr Richards)

27. Other sound effects…
Like light, sound can be…
1) Reflected – sound reflections are called
______.
2) Refracted – this is why you might sound
strange if you try talking underwater

28. The Ear
Label your diagram with the following:
These bones are vibrated by the eardrum
This tube carries the sound towards the eardrum
This part is used to help us keep our balance
This part “picks up” the vibrations
This part of the ear contains many small hairs with turn
vibrations into an electrical signal
This part connects the ear to the mouth
This part “channels” the sound towards the ear drum

29. The Ear