Transcript Light PowerPoint Presentation

Light and Sound
In this unit:
1)
2)
3)
4)
5)
6)
Properties of light
Reflection
Colours
Refraction
Properties of sound
Hearing
Part 1 – Properties of Light
Light travels in straight lines:
Laser
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
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.
We see things because they
reflect light into our eyes:
Homework
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
Shadows
Shadows are places where light is “blocked”:
Rays of light
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
Part 2 - Reflection
Reflection from a mirror:
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
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 !!!
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
Using mirrors
Two examples:
2) A car headlight
1) A periscope
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.
The colours of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet
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 red
and green
makes yellow
Adding blue and
green makes cyan
(light blue)
Adding all
three makes
white again
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
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
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
In different colours of light this kit would look different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue
Some further examples:
Object
Red socks
Blue teddy
Colour of light
Colour object
seems to be
Red
Red
Blue
Black
Green
Black
Red
Black
Blue
Green
Red
Green camel
Blue
Green
Red
Magenta book
Blue
Green
Using filters
Filters can be used to “block” out different colours of light:
Red
Filter
Magenta
Filter
Investigating filters
Colour of filter
Red
Green
Blue
Cyan
Magenta
Yellow
Colours that could be “seen”
Red
Blue
Green
Yellow
Cyan
Magenta
White
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
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
Drawing sounds…
This sound wave has a
_____ frequency:
This sound wave has a
___ _frequency:
Drawing sounds…
This sound wave has a
_____ amplitude
(loud):
This sound wave has a
_____ amplitude
(quiet):
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)
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
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
The Ear