Download What is Light?

Light : What is Light?
 Light carries energy
and travels as a wave.
 Light travels at
300 000 000 m/s or
300 000 km/s (much
faster than sound).
 Light waves travel in
straight lines.
© Boardworks Ltd 2003
© Boardworks Ltd 2003
© Boardworks Ltd 2003
Light : What materials will light travel
through?
 Hold different materials between the lamp
and the screen. Use the results table and
shading chart on the next slide to estimate the
opacity of different materials.
© Boardworks Ltd 2003
What materials let light through?
Material
Tracing paper
Opacity [%]
Shading chart.
100%
1 ply tissue
2 ply tissue
75 %
Smoked glass
50 %
Glass
30 %
Perspex
Wood
2.5 %
5%
10 %
15 %
25 %
20 %
0%
Opaque objects do not allow light to pass through
them - transparent ones do. Translucent materials only
let through part of the light.
© Boardworks Ltd 2003
How does light travel?
1)
Fill a clear glass trough or empty fish tank with
smoke.
2)
Shine rays of light through the tank and
describe what you see.

LIGHT WAVES TRAVEL IN STRAIGHT LINES.
© Boardworks Ltd 2003
Seeing objects
How do we see an object?
The light from the object enters our eye.
Do we see all objects in the same way?
There are two ways we see objects…..
• We see some objects by reflected light.
• We see other objects because they are light sources.
© Boardworks Ltd 2003
Light sources
How do light rays from a light bulb and
other light sources reach our eye?
They travel in a
straight line directly
into our eye.
© Boardworks Ltd 2003
Reflected light
How do light rays from a book and other such
(non-luminous) objects reach our eye?
Light from the lamp or
another light source
strikes the book and
some of the light is
reflected into our eye.
© Boardworks Ltd 2003
What happens to the light which isn’t
reflected?
• Some of this light may be absorbed (e.g. as
heat).
• Some of this may also be transmitted (e.g
glass reflects a small amount of light, absorbs
some of the rest and allows most of it to pass
through.
© Boardworks Ltd 2003