Class 6-10 Introduction to Light
…. So it’s horizontal over here. If you have the ray, incident ray, that comes down here, and if we have a normal that is perpendicular to this mirror, then this angle of incidence, which is called the angle made by the incident ray along with the normal, and there is another ray, the one that gets reflected, and that is called the reflected ray, and that has an angle called the angle of reflection. And these two angles, the angle of incidence and the angle of reflection are always equal. That is what is called the first law of reflection.
You all watch cricket matches, right ? I was watching this match… And this Muttiah Muralitharan… He walked up and he bowled a ball… And it bounced in a place and went off like that… Now one of the things we can understand is that in light doesn’t only do that.
What light does is we are going to throw it at one particular angle, that is if the angle of incidence is going to be here, then the angle of reflection is always going to be there. So it is not going to try and do that or try and do this. That is not going to happen. There is no spin bowling in the world of light. Light follows the rules. And one of the rules it follows apart from being the angle of incidence equal to the angle of reflection is that all these three lines. In other words, when I say there is no such spin bowling, the other way of saying it… The mathematical way of saying it… Is that the angle of incidence, the normal, and the angle of reflection all will lie in the same plane.
And what do i mean by all will lie in the same plane? If I take those three lines and put it on a table, all the three lines will be on the table. Not one will stick out, one of them will go off … Nothing will happen. So these two together, which says that the angle of incidence is equal to the angle of reflection, and the angle of the incidence ray, the normal and the reflected ray lie on the same plane, these two form the laws of reflection. And using these, we can solve / we can predict the behaviour of light in many ways as long as
you keep in mind the light to be a ray.