Light and Shadow
Light is form of energy and is very important in all
aspects of our lives. In the absence of light plants would not able to grow as
they require sunlight to prepare their food and in absence of plants, animal
and human would have nothing to eat.
We see with our eyes but we cannot see anything when
there is no light. We have noticed that in complete darkness no object is
visible to us.
Sources of light
Light travels from a light source.
Sun is the main source of natural light. Other forms of
natural light are other stars and moon. Star provides very less amount of light
at night because they are very far from earth compared to sun. Moon, especially
full moon provides little light at night but light from the moon is just light
reflected from the sun. Some animal also emit their own lights such as glow-worms,
fireflies and some fish.
Source of artificial light are burning wood, candles,
earthen lamps. Candle are made of wax, oil and wick are used in lamp to burn.
Now days we use electric bulb, tube and lamp as source of light.
are those which emit light of their own such as sun, stars and bulb. Non
luminous bodies are those which do not have their own light such as moon,
book etc. Non luminous object are visible to us when light from luminous object
falls on them.
Properties/Characteristic of light
- Light travels in a straight line
Light travels in a straight line in the form of
rays. It travels very fast at the speed of 300,000 km in a second! Light
does not bend, it can only be blocked. Light continue to travel in straight
line until it hits something else.
It is evident from shadow formation that light travels
in straight line.
Place an opaque object in the path of light. What do
We see dark area on other side because opaque object
has blocked the light from reaching to the other side. The dark area formed is
Take 4 square card of same size with hole punched in
the center of the cards. Place all 4 cards vertically on a table with the help
of modeling clay at an equal distance from each other such that holes of all 4
cards are in alignment. Now turn off the light in the room and place flashlight
at one end of the row of square cards placed on the table.
What do you observe?
We observe that the holes are in alignment and the
light travels in a straight line.
covers a large area when the source of light is far off. Similarly sun shines
high up in the sky and spreads its light all over.
reflects when it hits a surface
When light rays hits on any surface, it bounces back
(it reflect back). We are able to see objects because light rays enter our eyes
after bouncing off rough surface. A rough surface reflects or bounces off light
in all directions whereas smooth and polished surface bounces off light in one
direction. Therefore, mirrors are good reflectors.
Transparency of materials
Material that allows light to pass through them in
straight lines is called transparent material. Object on other side of
transparent material is clearly visible. Example: glass, crystal, clear plastic.
Material that allows some light to pass through them is
called translucent material. Object on other side of
translucent material is not clearly visible. Example: Tissue paper, frosted
glass, colored glass, butter paper, colored plastic.
Material that does not allow any light to pass through
them is called opaque material. Example: wood, metal, stone, our body.
Shadow is formed when light is not able to pass through
an opaque object. When an opaque object come in the path of the light, the
light falling on that object cannot reach the other side, therefore, that
particular region becomes dark. The rest of the area is lit as there is nothing
to stop the light from passing through.
The object must be opaque or translucent to make a
shadow. Opaque objects make dark shadows and translucent objects make faint
shadows. A transparent object will not make any shadow, as all light will pass
If we bring an object closer to the light source, the
shadow becomes bigger as it blocks more of the light rays and if we take an
object away from light source, the shadow becomes smaller as it blocks less
amount of light.
The Sun casts long shadows in the morning and
evening as the Sun is lowest in the sky. The Sun casts the shortest
shadows at midday, when the Sun is highest in the sky.
Lateral inversion is the reversal of image when placed
against plain mirror. It may also be referred as “mirror image”. This implies
that object on the right side appears on the left side in the mirror.