Page 60 - Science Class 6 Times Publication

Again, remove the glass and try to see through the oiled paper. Can
you see the burning candle clearly ?

What differences did you get while observing the burning candle
through different substances ?
Observation: You cannot see the candle through the book, but can
see clearly through the glass. You can see candle partially when
observed through an oiled paper.

Some substances allow light to pass through them easily, some allow
light to pass partially while most of the substances do not allow light
to pass through them.

The substances can be classied into transparent, translucent and
opaque on the basis of transmission of light through them.

The substances which allow light to pass through them easily
are called transparent substances. We can see clearly through
such substances. Ordinary glass, air, water and some plastics are
transparent substances.

The substances through which light can pass partially are called
translucent substances. We cannot see the things clearly but we can
see partially through such objects. Greased paper, waxed paper, some
plastics and ground-glass panes are some examples of translucent
substances.

The substances through which light cannot pass at all are called
opaque substances. We cannot see at all through such substances.
For example, book, wood, metals, stone, muddy water, etc.

Rectilinear propagation of light

Light can travel in different media such as air, water, glass, etc.
If light is traveling along the same medium, it always travels in a
straight line. This phenomenon is known as rectilinear propagation
of light.
Hence, the phenomenon in which the light travels in a straight line
through a same transparent medium is called rectilinear propagation
of light.

Times' Crucial Science and Environment 56 Book 6