Light...
ORB Education Quality Teaching Resources
 ORB Education
Visit http://www.orbeducation.com.au for the full,
editable versions with solutions.
ScP033 – Mixed PowerPoints
Consider the picture below…..
Belinda
Why can the Belinda see the cat, but not the
dog?
Let’s start at the beginning….
Light travels in straight lines
This is why we cannot
see around corners.
This is also the reason
why shadows occur
when something gets in
the way of the light.
How do we see things?
For you to be able to see an object, light must
travel from the object to your eye.
The light that hits the object usually comes
from somewhere else …
… maybe the Sun …
… or perhaps from a light bulb, candle or torch.
These are called ‘light sources’.
How do we see things?
So, in order to see an object, light must travel
from the source to the object
It must then be reflected off the object and
travel to your eyes.
So, looking at that picture again...
Belinda can see the
cat.
This is because
light from the
source can reach
the cat ...
… and the reflected
light from the cat
can travel in a
straight line to
Belinda’s eyes.
So, looking at that picture again...
Belinda can’t see
the dog.
Even though light
from the source can
reach the dog ...
… the reflected light
from the dog cannot
travel straight to
Belinda’s eyes.
Consider the picture below…..
Can the girl see the person in the mask?
On your worksheet, draw light rays in order to
determine whether she can or not.
And the answer …
No
Summary so far
• Light travels in lines that are …
… straight.
• Some things, such as the Sun and light bulbs
give out their own light. These are called …
… light sources.
Other examples of light sources are …
… candles and torches.
Summary so far
• Most things don’t give out their
own light. They simply …
… reflect the light that has come
from a source.
• For you to see the object, this
reflected light must be able to …
… travel in a straight line to your
eyes.
Reflection from Smooth Surfaces
A very smooth surface, such as a
mirror or a still pond, will reflect
a beam of light in one direction
only.
Mirror
A clear reflection is seen in the
surface.
This type of object is said to have a
glossy (or shiny) surface.
These thin
beams of light
are called
‘light rays’.
Reflection from Rough Surfaces
Most objects are not smooth,
especially when viewed under a
microscope.
In these cases, the light is
reflected in all directions.
A clear reflection is not seen in the
object.
This type of object is said to have a
‘Matt’ surface.
Surface of
Paper
(under a
microscope)
Which brings us to the Law of Reflection
Mirror
If a ray of light is
directed at a mirror …
… at a certain angle …
… it will be reflected
from the mirror …
… at exactly the same
angle.
700
700
Which brings us to the Law of Reflection
Mirror
Or, in more theoretical
terms:
angle of
incidence, i
Normal
angle of
reflection,
r
700
200
200
angle of incidence = angle of reflection
angle i = angle r
700
Drawing Rays
Show on your diagram what happens to the ray
of light next.
mirror
400
400
Press the Spacebar when you have finished.
Drawing Rays
… and this ray of light?
300
300
mirror
Press the Spacebar when you have finished.
The Pyramids
The law of reflection has been known for some
time.
In fact, the pyramids in Egypt were decorated by
people who understood it.
The artists working in the Pharaoh’s tomb needed
to have enough light to see their painting.
They didn’t use oil lamps or
candles, because that would
have left marks on the walls
from the dark smoke.
The Pyramids
So that light
could be
reflected into
each chamber,
polished metal
mirrors were
placed along the
corridors!
The light could
then reflect all
the way to the
artist in the
tomb.
The Pyramids
Unfortunately, each time light is reflected,
some of it is absorbed. The light intensity
would drop with each reflection.
The amount of light reaching the burial
chamber would have been very small.
The artists eyes, however, would have slowly
adjusted to the small amount of light.
When the artist left the tomb,
the daylight would have
seemed blindingly bright.
The Pyramids
In this way, the artist’s life was
dedicated to the Pharaoh.
Light Experiments
Claire is performing a light experiment.
Using a ray box, she sends a ray of light towards
a mirror.
mirror
ray box
100
100
She places a piece of paper underneath the ray
box and mirror, so that she can mark in the
direction of the ray before it strikes the mirror.
She can also trace the reflected ray.
Light Experiments
Claire carries out the experiment five times,
using different angles each time.
These are the angles she directed the ray from:
a. 100
b. 200
c. 300
d. 450
e. 600
Using this information, fill in the table on your
worksheet.
Light Experiments
This is the table that Claire completed after
measuring each of the angles.
Angle that light strikes the
mirror
Angle that light reflects
from the mirror
100
200
300
450
600
100
200
300
550
600
Which angle must Claire have recorded
incorrectly?
Answer: 450 / 550
Remainder removed from this sample presentation.
ORB Education Quality Teaching Resources
 ORB Education
Visit http://www.orbeducation.com.au for the full,
editable versions with solutions.
ScP033 – Mixed PowerPoints