Contents
8K Light
What is light?
Reflection
Refraction
Colour
Summary activities
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• Objective:
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•
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Success Criteria
To differentiate between specular and
diffused reflection.
To describe the law of reflection.
To illustrate how an image is formed in a
mirror using a ray diagram.
To prove the law of reflection by
conducting an experiment.
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Starter:
What does this say?
Why might it be written
backwards?
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Task 1: Differentiate between specular
and diffused reflection.
To know how light rays can be
reflected.
Shiny smooth surfaces reflect
regularly, other surfaces also reflect
light but if the surface is rough the
light is reflected in all directions. We
call this diffuse reflection.
Smooth or gloss
surface. (Mirror,
glass or still body of
water)
Rough or matt
surface. (bricks,
wood, wall paint or
skin)
Reflective materials
Objects that reflect light well:
 Have smooth, shiny surfaces
and are usually pale colours.
 Give clear images because
they reflect light regularly.
Objects that do not reflect light well:
 Have rough, matt surfaces
and are usually dark colours.
 Give diffuse images (or
do not give any images)
because they reflect light
irregularly.
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Specular
reflection
Allows us to see
ourselves
Diffused
reflection
Allows us to see
everything
Specular
reflection
Diffused
reflection
Task 2: To describe the image formed
in a plane mirror.
The virtual image
The reflection seen in the plane mirror is known as
the virtual image. It is:
TASK: Write down your
 the same shape
name. Show how the
 the same size
mirror reflection will
 the same distance apart look like.
 left and right side are swapped
Why does the ambulance
have the sign reversed?
Why is this mirror helpful?
Describing images – real or virtual?
When we look into a mirror we
see an image. The image
appears to be behind the mirror.
If you look behind the mirror,
the image is obviously not
there, so we say it is a
virtual image. A virtual
image is one which cannot
be formed on a screen.
A real image is one that can be
formed on a screen, such as the
real image from the projector,
which you are reading now!
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What is lateral inversion?
A plane mirror reflects light
regularly so it produces a
clear image, which is the
same size as the object.
The image appears the
same distance behind the
mirror as the object is in
front of it.
What is different about the
image compared to the object?
When an object is reflected in a plane mirror, left appears
as right and right appears as left. This type of reversal is
called lateral inversion.
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Describing images – orientation
If the rays of light from
the top and bottom of
an object cross over
before an image is
formed, the image will
appear upside-down.
This is an inverted image.
Inversion can also occur if rays from the
right and left of an object cross over.
This is known as lateral inversion and
is seen most commonly in plane mirrors.
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Images in plane mirrors
c
ca
ta
t
If we look into a mirror, we see an image.
What kind of image is formed in the plane mirror?
 laterally inverted
 same size as the object
 virtual
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Describing images – quiz
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Task 3: Differentiate between reflect, refract,
transmit and absorb.
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Reflection investigation
1. Fix a plane mirror to a piece of
paper and draw around it.
2. Draw a normal (at 90°) through
the centre of the mirror outline.
3. Use a ray box to shine an
incident ray at the mirror – plot
the incident and reflected rays.
4. Measure the angles of
incidence [i] and reflection [r]
and record the results.
angle i
angle r
Angle of
Angle of
incidence [i] reflection [r]
5. Repeat for another four angles
of incidence.
6. What do the results show?
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Task 4: Describe the laws of reflection.
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The Law of Reflection
Incident ray - the ray of light that hits the surface of the mirror.
Reflected ray - the ray that reflects of the mirror.
Normal - an imaginary line at 90˚ to the mirror.
Angle of incidence – angle between the incident ray and the normal.
Angle of reflection – angle between the normal and the reflected ray.
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Reflection ray diagram
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Using reflection
Reflection can be very useful.
High-visibility strips are very
reflective and make sure that
this cyclist gets noticed when
there is little light.
How does a periscope use
reflection?
The two plane mirrors must be
positioned at 45° to each other.
Light is reflected at right angles
from the top mirror onto the
bottom mirror and into the eye
of the viewer.
Where are periscopes used?
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The law of reflection in action
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Plenary : Reflection summary
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Reflection – true or false?
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