Facts about Light
■
■
It is a form of
Electromagnetic Energy
It is a part of the
Electromagnetic
Spectrum and the only
part we can really see
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
-The Sun
- Lamps
- Lights
- Lasers
- Campfires
Reflectors
-The Moon
- Mirrors
- People
- Objects
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
THE SAME 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
Using mirrors
Two examples:
2) A car headlight
1) A periscope
Plane
Suppose Mirror
we had a flat , plane mirror mounted vertically. A candle is
placed 10 cm in front of the mirror. WHERE IS THE IMAGE OF
THE CANDLE LOCATED?mirror
On the surface of the mirror?
Behind the mirror?
Object Distance, Do = 10 cm
Same side as the object?
Plane
Mirror
Suppose we had a flat , plane mirror mounted vertically. A candle is
placed 10 cm in front of the mirror. WHERE IS THE IMAGE OF
THE CANDLE LOCATED?
mirror
Object Distance, Do = 10 cm
Virtual Image
Image Distance, Di = 10 cm
Do=Di, and the heights are equal as well
Virtual Images are basically images which cannot be
visually projected on a screen.
If this box gave off
light, we could project
an image of this box
on to a screen
provided the screen
was on the SAME
SIDE as the box.
You would not be able to project the image of the
vase or your face in a mirror on a screen, therefore
it is a virtual image.
CONCLUSION: VIRTUAL IMAGES are ALWAYS on the OPPOSITE side of
the mirror relative to the object.