Reflection of light

Reflection of light

You know that light is a form of energy. is energy travels from a source in all direction and the direction along which it travels is called a ray of light. Observe a bulb in your house, slightly closing your eye lids. You can see the light in the form of yellow lines. One such a line is called a ray. A bundle of such rays constitute a beam of light.

Light falling on any polished surface such as a mirror, is reflected. This reflection of light on polished surfaces follows certain laws and you might have studied about them in your lower classes. Let us study about them little elaborately.

1. Lows of reflection

Consider a plane mirror MM′ as shown in Figure 1. Let AO be the light ray incident on the plane mirror at O. The ray AO is called incident ray. The plane mirror reflects the incident ray along OB. The ray OB is called reflected ray. Draw a line ON at O perpendicular to MM′. is line ON is called normal.

The angle made by the incident ray with the normal (i = angle AON) is called angle of incidence. The reflected ray OB makes an angle (r = angle NOB) with the normal and this is called angle of reflection. From the figure you can observe that the angle of incidence is equal to the angle of reflection. (i.e) i = r. Also, the incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. These are called the laws of reflection.

Reflection of light has many interesting facts. Let us look at some of them here.

How tall does a mirror have to be to fit your entire body?

Can you see your entire body in a make-up mirror? Now, stand before the mirror in your dressing table or the mirror xed in a steel almirah. Do you see your whole body now? What do you know from this? To see your entire body in a mirror, the mirror should be atleast half of your height. Height of the mirror= Your height/2

Find out

Using a metre scale, measure your height in centimetre. Now find out the height of the mirror to see your entire body.

2. Lateral inversion

You might have heard about inversion. But what is lateral inversion?The word lateral comes from the Latin word latus which means side. Lateral inversion means sidewise inversion; it is the apparent inversion of left and right that occurs in a plane mirror.

Why do plane mirrors reverse left and right, but they do not reverse up and down?

Well the answer is surprising. Mirrors do not actually reverse left and right and they do not reverse up and down also. What actually mirrors do is reverse inside out.

Look at the image below and observe the arrows, which indicate the light ray from the object falling on the mirror. The arrow from object’s head is directed towards the top of the mirror and the arrow from the feet is directed towards the bottom. The arrow from left hand goes to the left side of the mirror and the arrow from the right hand goes to the right side of the mirror. Here, you can see that there is no switching. It is an optical illusion.

The apparent lateral inversion we observe is not caused by the mirror but the result of our perception.

Note: You can try this activity with pencil or pen. What do you observe?