1. WHAT IS LIGHT AND WHAT ARE ITS PROPERTIES?
Light is one of the most mysterious things on the world. We don’t see light, we in fact, see because of it. Anything heated becomes luminous, is itself glowing, and enables us suddenly to see things around it. If you are sitting in a dark room, by an can’t see anything. When you switch on the light, the bulb glows and other objects are seen! How, what is happening? Clearly the bulb is the source of light and if we close our eyes, we can’t see, obviously. Something mysteriously is happening between the source of light (here bulb) and our eyes.
What is it?
Something is travelling between the source and our eyes. And this something seems to travel on straight lines. Otherwise why would there be shadows if anything obstructs that something coming from the source of light. (here bulb) Then, there are colours. It is as if light comes in a variety of colours. A red short is red, may be, because that mysterious something is a type that causes the sensation of red.
Red is red. We can’t question it. It is that particular quality. What we are doing here is trying to ask what causes red. That which causes on us the sensation of red is “red light”. In the same way violet light, yellow light, blue light, green light, indigo light, orange light.
What about black colour and white colour. White is a mixture of all colours and black is that which gives off no colour. When light, that invisible thing, falls on a particular object, the object absorbs some colours and gives off a colour. The colour given off, if red, will make us see red. Similarly with other colours. If the object gives off all colours, we see white. If the object absorbs all colour and gives off no colour, we see black.
If the object lets the light pars through completely the object is not seen eg: glass, water. What if the object does not take anything and reflects the light from an object completely. Then it becomes a mirror!
See the figure. The light from object A travels on straight line and hits the mirror. The mirror doesn’t take anything and simply reflects it and then it reaches our eye. Now comes the catch!
What do we see! Since all the light from A has reached us, we see A but where do we see A?
From childhood our brain knows only to ‘see’ objects in straight lines. So it sees the object at A as shown on the figure!
See figure(2) the object itself has the eye. Then we see ourselves at a obstance which the same distance ‘d’ but ‘inside’ the mirror! In a way the objects that we see is a hallucinatism but it is a hallucination due to physics and it’s reality not due to a ghost! Let us now consider another and last strange phenomenon that we see with our naked eye.
Why does the win in a glass of water appear to be above than it’s normal bottom? Why does a stick seem to bend in water? The answer is that light bends when travelling from one medium to another. (Here from water to air). So what? What if it bends?
If we take two rays - ray 1 and ray 2 and if it bends and reaches our eyes, our eyes don’t know that. It sees on straight lines only and that means that it hallucrates and sees the object above than the normal. Even the bottom comes up.
A spom bends and bulges from the same reason.
So these facts give us some ideas about light which are fairly obvious. But it is a wonder, isn’t it?
Its strange - this thing that travels in straight lines, bends when travelling from one medium to another, is composed of various components which cause various sensations of colours in us!
Light travels in straight lines
Light consists of various colours
Light is reflected from norms
Light is refracted (as it is called, the act of bending) when from one met to another.
When Light strikes one face of a prism, the different colours of light refract by different amounts! Thus they emerge from the other face with the colours separated. Rainbows are formed that way (the raindrop acts as prism)
The principle of refraction is used in lenses to make things bigger.