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.
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
travels from a light source.
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.
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.
bodies 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
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
is evident from shadow formation that light travels in straight line.
an opaque object in the path of light. What do you observe?
see dark area on other side because opaque object has blocked the light from
reaching to the other side. The dark area formed is the shadow.
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.
do you observe?
observe that the holes are in alignment and the light travels in a straight
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.
Light reflects when it hits a surface
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
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.
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.
that does not allow any light to pass through them is called opaque
material. Example: wood, metal, stone,
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
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 through it.
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.
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.
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.