Form of energy that helps us to see the object. Until and unless light falls on object and gets bounces back from it, we are unable to see that object. Remember, ‘Mr. India’ the most iconic movie of India, in which the hero of movie gets invisible due to certain gazette which does not allows the light to bounce back from the body of hero. You may have seen very often, the beam of light coming through window or a small opening in it, sharp and focused beam of light formed by torch/headlights of vehicle. Have you handled the LASER gun ever? How does it travel? You had some activities to study the path of light in grade VI. What can you recall from the activity in which you have observed the candle through the bent pipe? What if you replace the bent pipe with straight one?
Following are some characteristics of light.
- Light always travels in a straight line.
- We can change the path of light by striking it on different surfaces.
- Light has unidirectional nature, hence we use the term “ray of light” to indicate the direction of propagation of light.
- Group of parallel rays is called as ‘beam of light’.
- The light with single colour is called as ‘monochromatic light’.
- Light posses some important phenomena such as reflection, refraction, dispersion and many more.
- The branch of physics which deals with study of light and instruments based on light is called as Optics.
Reflection of Light
What do you see when you stand in front of mirror? Why the letters of the word ‘AMBULANCE’ is written inverted on ambulance van? When you look towards silent pond of water why it appeared to be shine? Answer of all of these questions lies in the concept of reflection of light.
There are two types of material available around us when we deal with light, viz.
i) Opaque–which does not allows light to pass through it. E.g. mirror,shiny metal surface etc.
ii) Transparent –which allows light to pass through it. E.g. glass, water etc.
When light falls on plane/smooth and shiny surface, it bounces back this is called as reflection of light. We can see the object due to reflection only. When light falls on any non transparent object, it gets bounced back and enters in our eyes, which gives us the sensation of vision of that object. The direction of light can be changed by reflecting it from polished surface.
Take a look on the diagram shown beside for better explanation of reflection of light.
Suppose we have smooth/shiny surface like mirror at which light is strike as shown in fig.
- The ray of light directed towards surface and strikes at a given point is known as Incident ray.
- Perpendicular drawn to the given surface as reference line is called as Normal.
- The ray of light which bounces back from the surface is known as reflected ray.
- The angle made by incident ray with normal is called as angle of incidence (i).
- The angle made by reflected ray with normal is called as angle of reflection (r).
As shown in fig. above, when ray strikes the polished surface make angle (i) with normal, gets reflected back but not in the same direction. The path of light is changed after reflection. Rays follows certain fixed path which is based on laws of reflection, states as follows.
Laws of reflection:
Incident ray lies on opposite side of normal and all three i.e. incident ray, reflected ray and normal lies in same plane at the point of incidence.
Angle of incidence is equal to angle of reflection (i=r)
The laws of reflection are always whenever image is formed by mirror.
Q. What do you mean by light?
Ans: Light is form of energy that helps us to see the object.
Q. Define reflection of light.
Ans: When light falls on plane/smooth and shiny surface, it bounces back this is called as reflection of light.
Q. Define normal.
Ans: Perpendicular drawn to the given surface as reference line is called as Normal.
Q. State the laws of reflection.
Ans: 1. Incident ray lies on opposite side of normal and all three i.e. incident ray, reflected ray and normal lies in same plane at the point of incidence.
2. Angle of incidence is equal to angle of reflection (i=r)
Q. How we can change the path of light?
Ans: The path of light is changed after reflection of light from any polished surface.
md muzammil