It is a matter of common experience that the objects inside a dark room, which are invisible, become visible when the room is illuminated by a source of light. Thus light can be defined as the external cause responsible for the sensation of vision.
In the previous chapter we have seen how light gets reflected when it is incident on a surface. Now let us see what happens when a ray of light traveling from one medium to another medium of different density.
It is a matter of common experience that precious stones like diamonds, rubies, etc. or glass pieces glitter when light, particularly white light is incident on it. In this chapter let us find out why white light incident on a transparent prism splits into different colors.
The previous chapter dealt with the refraction of light by lenses and also about the formation of various types of images by a lens for different positions of the object. In this chapter let us find out how lenses are used in optical instruments like microscopes and telescopes to obtain magnified image of an object.
Appliances used in our day to day life are based on the principles of electricity and magnetism. Electricity is one of the most important sources of energy. Lights, fans, motors, radios and television are some common appliances which work on electricity.
Man is surrounded by an ocean of energy. Mankind has tapped only a fraction of it. The most colossal dynamo of all is the sun, an unimaginable vast powerhouse which affects everything on earth. From time immemorial man has learnt to harness this energy. In 100 B.C. Romans used coal as a fuel to produce fire. In 650 B.C. windmills were used to help travel from place to place. Steam engines later replaced horses and developed into locomotives as modern means of transport.
It was once believed that the earth was the center of the universe and that everything moved around it. It was later discovered that the earth moves around the sun.
In the second century AD a Greek writer named Lucian wrote a story about a trip to the moon. He did not even know how far the moon was but his story revealed that the idea of space travel was certainly not new.
You have learnt in the earlier chapters that flow of electrons constitutes an electric current and current can be generated from a battery or a generator. Scientists later discovered that there are many other ways of producing the stream of electrons.