Download SNC 2D Notes: Properties of Light How Do We

SNC 2D Notes: Properties of Light
How Do We See
We can see objects in one of two ways:
1. By the light emitted by the object – said to be luminous
2. By the light reflected by the object – said to be non-luminous
Note: Any object we can see is called a source
Transmitted, Reflected and Absorbed
Light can be affected in three different ways when it strikes
different kinds of matter. It can be transmitted, reflected or
absorbed. A substance such as air allows light to pass through it,
almost as if it were not there. When light passes through a
substance, it is said to be transmitted through it. Any substance
that transmits light is called a medium
Other substances cause light to bounce off or reflect from them.
Example, mirrors, snow, white paper, etc, while other substances
absorb the light that strikes them. For example black surface such as
asphalt absorbs most of the light energy that strikes it. This light
energy is converted into heat energy, which accounts for heating of
asphalt on a sunny day.
Other Properties Of Light
i)
Light requires no medium to travel, and thus can travel in
empty space.
ii)
Light spreads out in all directions from the source.
iii) Light travels in straight lines as long as the composition of the
medium remains
constant. This property of light is called linear propagation.
Time Out Young One
What do you think would happen if light did not travel in a
continuous straight line?
You can get some idea by trying to judge the position of objects
under water when you look at them. Water and air are different
media, and as a result of this, light changes direction as it enters
and leaves the water at an angle. This results in a stick partially
immersed in water appearing bent, and objects under water
appearing closer to the surface than they actually are.
“All right enough “chilin” back to some hardcore science”
iv) Light is invisible when it travels through a vacuum or a
transparent substance. Since we are unable to see light as it
travels through air, we can only detect its presence by the
effects it produces.
v)
Light reflects off of surfaces. Among other things, this gives
rise to the images
we see in mirrors.
a) There are two types of reflection, regular and diffuse
reflection.
 Regular Reflection: occurs when light rays strike a smooth surface
and reflects in the same direction, staying parallel to one
another.
 Diffuse Reflection: occurs when light rays reflect off a rough or
uneven surface, they do not remain parallel but are scattered
in different direction.
vi) Light refracts, which means that it bends when passing from
one medium to
another. This property to light makes the straw appear bent
when viewed in the
water.
vii) Another aspect of light that is quite common is the dispersion
or breaking up
of white light into its constituent colours. For example, if a
beam of white light
enters a glass prism, what emerges from the other side is a
spread out beam of
many coloured light.
viii) The speed of light in vacuum has been measured to be 3.00 x
108 m/s. This is
the fastest that anything has been observed to move. At that
speed it would
take light a mere one tenth of a second to circumvent the
globe. [Scientist working
on the Large Hadron Collider in Geneva Switzerland believe they
have observed
neutrino particles travelling faster than light. ] When light
enters any material, it
slows down. The amount that it slows down depends on the
nature of the material.
The more dense the material, the slower the speed of light. For
example, in water,
light is approximately 30% slower than in vacuum, while in glass
it is 50% slower.
In diamond, one of the most dense material known, light travels
at less than 150
million meters per second.