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