Types of beam of light
Generally light is not a single ray,
but a bundle of rays which are called as a beam of light.
A light beam can be a bundle of
parallel rays, convergent rays or divergent rays. Let us look at the light
coming from the Sun. The rays of sunlight are parallel. Often the headlight of
car gives parallel rays. However look at the rays of light coming out of a
candle. Light rays go in all directions, from the candle fire. These rays are
divergent. Light rays from a flash light is also divergent. Using lenses we can
converge light rays. Using a lens, you can focus sunlight at a point. That is
what we are making the light rays to converge.
Speed of light:
When lighting a bulb in a dark room,
light spreads the whole room quickly. This is because the light travels very
fast. Light travels three lakh kilometers per second in air or vacuum. In theory
, nothing can travel faster than light
Interaction of light with matter
Take a piece of clear glass, a paper
and a metal sheet. Shine a light from one side of each object and see if the
light penetrate on the other side. Readily, we can see light enters and comes
out of the other end of clear glass, whereas the light is bit dim through a
paper. Light does not pass through metal sheet. Depending upon permeability,
materials can be classified into three categories.
Materials that allow light to pass
through completely are known as transparent material.
Example: Eye glasses, clear drinking
glass, clear water,
face glasses used in buses.
Objects that allow light to pass
through partially are called translucent material. For example, we cannot see the image of
someone who stands behind a rough window glass, because it allows only a part
of light from the person.
Materials that are not able to allow
light to pass through, are called opaque material. Example: Wall, thick
card board, stone, etc.
transparent material, translucent material and opaque material among the given
(Clear plastic ruler,
cellophane paper , some water in a glass jar, tissue paper, drinking glass,
beaker, tap water, kerosene, coconut oil, note paper, card board, milk, diluted
milk, aluminum foil, thick colored plastic lid, rough glass piece, measuring
glass with water, wooden piece)
Place all the materials given above in the dark room. Focus a torch light on one side of each material. Inspect the light coming out at the other side of each material and then classify the materials in the table.