Question

According to laws of reflection, angle of incidence is equal to the angle of reflection. In what condition is this statement true?
A) It is always true
B) It is true sometimes
C) This is true only under special conditions
D) It can never happen

Answer 1

Hint: Reflection refers to the phenomenon of change in path of light without any change in the medium, in which the light is travelling. There are two universal laws for reflection of light from a polished surface. Universal laws do not change at different times.

Complete step by step answer:
Reflection is defined as the phenomenon of change in path of light without any change in medium. Suppose a light ray falls on a polished surface like a mirror, the light ray, on touching the surface of the mirror, changes its direction, without any change in the medium. This suggests that the light ray gets reflected to the same medium through which the incident light was approaching. The following figure can be used to clarify the above explanation.

There are two universal laws regarding reflection of light from a polished surface. They are as follows:
a) Angle of incidence is equal to angle of reflection. In the figure given above, angle of incidence is the angle made by the incident light ray and the normal drawn to the mirror, at the point of incidence. Similarly, angle of reflection is the angle made between the reflected ray and the normal drawn to the mirror, at the point of reflection. Clearly point of incidence and point of reflection are the same and is nothing but the point of contact, at which the incident light falls on the mirror surface.
If angle of incidence is denoted as $i$ and if angle of reflection is denoted as $r$, according to the first law of reflection,
$i=r$
b) Incident ray, reflected ray and normal to the mirror, all lie in the same plane. This law suggests that the phenomenon of reflection occurs in the same plane. In the figure, $AB$ represents the incident ray, $BC$ represents the reflected ray and $BD$ represents the normal to the mirror, drawn at the point of contact between the light ray and the mirror.
According to the second law of reflection,
$AB,BC$ and $CD$, all lie in the same plane.
Since both these laws are universal and true for all the mirrors at all the times, option A is the correct
answer.

Note:
Suppose the light ray is incident normally to the surface of the mirror, the light ray retraces its path, on reflection. Here, angle of incidence as well as angle of reflection is equal to zero.
$i=r=0{}^\circ $
Students should also be aware that an image formed by reflection from a plane mirror is virtual, erect and at the same distance behind the mirror as the object is in front of the mirror.