Unit :-7
Properties And
Behaviour of light
7.1 Luminous and non-luminous objects
Luminous objects
In our daily life, we see that some objects like the Sun, stars, lighted bulb, torch, and lighted candle, etc., emit their own light. The Objects thats produce Their light, are called luminous objects.
In complete darkness, we can see different objects around us. Why it happens? Human eyes get the light reflecting from different luminous objects. This reflecting light helps us to see things around us.
To be able to emit light, the luminous object, must have its own source of light. For example, a torch shines because of chemical energy stored in its battery.
All the stars shine using energy created by chemical reactions.The Sun is the largest Source of light.It emits light as a result of nuclear reactions.
Non-Luminous objects
In our daily life, there are many things that we cannot see in the dark. This is because they do not emit their own light. The objects like books, chairs, tables, bags, shoes, trees, moon, etc., do not emit their own light.
The objects that do not emit their own light are called non-luminous objects We can see non-luminous objects only when light falls on them from a luminous object and reflects into our eyes.
The Moon and the planets are the examples of non-luminous objects.They reflect light coming from the Sun and become visible.
7.2 Transparent,opaque and translucent objects
From this activity, we conclude that there are three types of non-luminous objects on the basis of optical properties.
i. Transparent objects
The objects through which light passes easily are called transparent objects.Clear glass, clear water, and glass etc., are examples of such objects.
li. Translucent objects
The objects through which some of the light can pass and most of the light is blocked are called translucent objects. Frosted glass, coloured plastics, tracing papers and tissue papers are the example of such objects.
We can see these things, but not clearly. Light is blurred after passing through these objects.
iii. Opaque objects
Objects through which light cannot pass easily are called opaque objects. They block all light and do not allow it to pass.
We cannot see through these objects. Objects made up of wood, metal, and bricks are examples of opaque objects.
7.3 Properties of light
Light is a form of energy. When its hits something light an object, it is reflected. Light travels in a straight line. When an object is placed in its path, it casts shadow of an object.
When light comes from the Sun, if it is blocked, eclipses are formed. These are the properties of light. Let us learn the properties of light in detail.
Light travels in a straight line
Light always travels in a straight line. It means that when light is emitted from a source, it chooses such a path which is short and has least obstacles.
The shortest path selected by light is called a straight line. The entrance of light beam in the room through a hole, passage of light through dense trees and visibility of light beam from a torch etc., shows that light always travels in a straight line.
