Question

Which mirror should be used to obtain a parallel beam of light from a small lamp?
A. Plane mirror
B. Convex mirror
C. Concave mirror
D. Any of the above

Answer 1

Hint: Bundle of rays is called a beam of light. Light travels in a straight line path called a ray of light. If the aperture of the mirror is too big the beam gets spread out.

Complete Step-by-Step solution:
Spherical mirror is the mirror whose reflecting surface is part of a sphere. There are two kind of mirror:
Concave mirror and convex mirror. We know that light coming from lamps diverges i.e if the aperture of the mirror is too big the beam will spread out. Due to this concave mirrors of parabolic shapes are used, these have a slightly different shape to the spherical mirrors and will give a perfectly parallel beam. Consider the diverged beam of lamp on a concave mirror. The rays diverge and incident on the concave mirror and it gets reflected in a parallel way.
After reflection the point where light rays merge is called focal point. So when the lamp is on focus then only a parallel beam of light is obtained from the small lamp.

Addition information:
The law valid to any reflecting surface for the following conditions-
1. The angle of reflection is equal to the angle of incidence.
2. The incident ray, the reflected ray and normal to the reflecting surface, lie in the same plane, at the point of incidence.
3. The incident ray, the reflected say lies on the opposite sides to that of normal.
Correct Option is (C).

Note: If parallel beams are incident at some angle with the principal axis, the reflected rays converge at a point in a place through the focal point normal to the principal axis. After says get reflected, it will concentrate on a point called focal point.