Properties of waves

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Properties of waves
Wave shape
peak
trough
Wave key words
Wave key words:
•Wavelength – length of one complete wave, measured in metres (m). It is
usually taken from the top of one peak to the top of the peak on the next
wave.
•Amplitude – the height of the wave, usually taken from an imaginary line
drawn directly through the middle of the waves, up to the peak. The bigger the
amplitude, the greater the amount of energy a wave will have.
•Peak – the highest point of a wave.
•Trough – the lowest point of a wave.
•Frequency – the total number of complete waves that pass a given point,
every second. It is measured in hertz (Hz).
Wave equation
Reflection - Lateral inversion
A plane mirror reflects light regularly so that it produces a clear image
which is the same size as the object.
What is different about the image?
When something is reflected in a plane mirror, left becomes right and right
becomes left. This is called lateral inversion.
Reflection
Circle the correct ray: A, B or C.
A
B C
Label the ray diagram to show the following:
Angle of Incidence
Angle of Reflection
Normal
Mirror
A
B C
A
B C
Reflection summary
1. Pale and shiny surfaces are good reflectors,
dark and rough surfaces are not.
2. The image in a plane mirror is laterally inverted.
3. The image is the same distance behind the mirror as the
object is in front.
4. The image in a plane mirror is the same size as the object.
5. The law of reflection is:
angle of incidence (i) = angle of reflection (r)
Refraction
Refraction
The speed of light waves depends on the material they are travelling through.
air = fastest
glass = slower
diamond = slowest
If light waves enter a different material (e.g. travel from glass into air) the
speed changes.
This causes the light to bend or refract.
air
glass
Refraction at the air-glass boundary
Refraction
Refraction
Refraction
Travelling through different materials
If you were running along a beach and then ran into the water when
would you be moving slower – in the water or on the sand?
In the water.
In a similar way, as light moves from one medium to another of different
density, the speed of light changes.
Do you think light moves faster or slower in a more dense medium?
Light moves slower through a more dense medium.
The speed of light in different media
Perspex
Speed of
light
(thousands
km/s)
Water
From this bar chart, which material do
you think is denser, Perspex or water?
300
270
240
210
180
150
120
90
60
30
0
Vacuum
Light travels at 300,000 km/s
in a vacuum.
As light enters denser media,
the speed of light decreases.
Perspex must be denser than water because light travels more slowly
through Perspex than water.
Why does light change direction?
Imagine a car driving from the road into a muddy field.
 In the muddy field it slows down as
there is more friction.
 If it enters the field at an angle then the
front tyres hit the mud at different
times.
road
tyre 1
 Tyre 1 hits the mud first and will move
more slowly than tyre 2. This causes the
car to turn towards the normal.
 When the car leaves the mud for the
road, tyre 1 hits the road before tyre 2
and this causes the car to turn away
from the normal.
mud
tyre 2
Apparent depth
The rays of light from a stone get bent (refracted) as they leave the water.
Your brain assumes these
rays of light have travelled in
straight lines.
image
Your brain forms an image at the
place where it thinks the rays have
come from – the stone appears to
be higher than it really is.
actual location
Materials and light
Transparent Light
Examples of
Transparent Materials
• Materials that you
can see through
allow almost all of
the light to pass
through.
• Light is allowed
through with very
little bending or
scattering of the
rays of light.
• Clear glass
• Clean water
• Clear plastic
Materials and light
Translucent Light
• Materials that
allow only some light
to pass through.
• Objects allow light
to pass through, but
they scatter the rays
so much that you
cannot get a clear
view of what is on
the other side.
Examples of
Translucent Materials
•Thin fabrics
•Frosted glass
•Thin paper
Materials and light
Opaque Light
•Light cannot pass
through these
materials.
Examples of Opaque
Materials
•Brick
•Metal
•Thick paper
•Aluminum Foil
•Wood
•Stones
Materials and light
Quick Facts about Opaque Materials
•These objects will cast a
shadow when lit up.
Ray of light
•Brick, metal, and thick
paper stop light
completely.
•We say the light has been
absorbed.
Opaque
brick wall
absorbs all
the light
No light is
transmitted
through the wall
White light
Splitting white light into colours
A prism splits a ray of white light into a spectrum of colours.
This is known as dispersion.
When white light is split, the colours always follow the same order.
Use this phrase to remember the order of colours:
Richard Of York Gave Battle In Vain
Dispersion
Each of the colours of the spectrum [ROYGBIV] has a slightly different wave.
What is the difference?
Each colour has a different wavelength ().
Dispersion
The different colours of light have different wavelengths, this means they
are bent (refracted) by different amounts.
Which colour is refracted the most?
Red light is refracted least
because it has the longest
wavelength.
Violet light is refracted the
most because it has the
shortest wavelength.
Colours of the spectrum
Absorption of light
Seeing colours
How do you see non-luminous objects
such as a book?
You see a non-luminous object
when light hits the object and is
then reflected into your eyes.
So how do we see different colours?
Why does a red dress look red?
Why does a green apple look green?
Primary colours animation
Primary and secondary colours
Colours are made by mixing other colours of light.
There are three primary colours of light used to make all other colours.
What are these colours?
The three primary
colours of light are red,
green and blue.
green
red
magenta
blue
The colours made by mixing two primary colours are called
the secondary colours – magenta, yellow and cyan.
Which primary colours?
Coloured objects in white light
Reflection and absorption of light
• Opaque objects reflect and absorb light.
• The color of an opaque object is the color
it reflects. It absorbs all the other colours.
This apple reflects
red and absorbs
all other colours.
Coloured objects in white light
Reflection and absorption of light
• Opaque objects reflect and absorb light.
• The color of an opaque object is the color
it reflects. It absorbs all the other colours.
•
•
•
The red pepper reflects red light and
absorbs all the other colours.
The green pepper reflects green light and
absorbs all the other colours.
The yellow pepper reflects yellow light
and absorbs all the other colours.
COLOURED OBJECTS
White object in white light
Object
appears
white
N
All colours
reflected
White objects reflect all colours and
absorb none
OBJECTS IN COLOURED LIGHT
White object in blue light
Object
appears
blue
N
Blue light
reflected
White objects reflect all colours and
absorb none
OBJECTS IN COLOURED LIGHT
White object in red light
Object
appears
Red
N
Red light is
reflected
White objects reflect all colours and
absorb none
OBJECTS IN COLOURED LIGHT
Red object in red light
Object
appears
Red
N
Red is
reflected
Red Objects reflect red light
OBJECTS IN COLOURED LIGHT
Red object in blue light
Object
appears
black
N
No light is
reflected
Red Objects reflect red light and
absorb all others
THE FRUIT BOWL IN WHITE LIGHT
A red apple
A green pear
A white plate
THE FRUIT BOWL IN RED LIGHT
A red apple
A green pear
A white plate
THE FRUIT BOWL IN BLUE LIGHT
A red apple
A green pear
A white plate
Coloured filters in white light
A coloured filter will allow it’s colour to be transmitted through
the filter, while absorbing all the other colours of white light.
Coloured filters in coloured light
A coloured filter will allow it’s colour to be transmitted through
the filter, while absorbing all the other colours of white light.
FILTERS white light – red filter
FILTERS white light – blue filter
FILTERS blue light – blue filter
FILTERS blue light – red filter
FILTERS white light – red and blue filter
Coloured light activity – instructions
The next two slides include a girl wearing a t-shirt and trousers.
The girl is standing in a different coloured light each time. The colour of this
light is written at the top of the slide.
The aim of each activity is to decide what colours the girls’ clothes would
appear in each type of coloured light.
Drag the correct t-shirt and trousers onto the girl to find out if you have
selected the correct colours.
Coloured light activity 1
Coloured light activity 2
Flag colours in different coloured light
How would the colours in this flag appear under these lighting conditions?
a) red light
b) green light
c)
blue light
What colour does it appear?
What colour does each object appear under the given lighting conditions?
Object (Colour) Colour Filter
red ball
red
red ball
blue
blue book
green
blue book
magenta
green apple
cyan
green apple
magenta
red and blue tie
red
Appearance
red
black
black
blue
green
black
red and black
Sound Word Search
Find the eight sound related words and match
them to their meanings. One has been done for you.
Light Puzzle
Anagrams
Multiple-choice quiz
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