Question

State four points of difference between a concave mirror and a convex mirror.

Answer 1

Hint: First, understand the meaning of a concave mirror and a convex mirror. Then understand the definitions related to the curved mirrors. The relation between the positions of the object and its image is given by ${\displaystyle \frac{1}{u}}+{\displaystyle \frac{1}{v}}={\displaystyle \frac{1}{f}}$.

Complete step by step answer:
The most common type of curved mirror is a spherical mirror. A spherical mirror has the shape of a section from the surface of a hollow sphere. If the inside surface of the mirror is polished, it is a concave mirror. If the outside is polished, it is a convex mirror.
Before stating the difference between a concave mirror and a convex mirror, let us understand a few definitions.
1) Pole (P) : It is the midpoint in the mirror.
2) Centre of curvature (C) : It is the centre of the sphere of which the mirror is a part.
3) Radius of curvature (R) : It is the distance between the pole of the mirror and the centre of curvature.
4) Principal axis : A line passing through P and C i.e. pole and the centre of curvature.
5) Focus (F) ; It is an image point on the principal axis for which the object is at infinity.
6) Focal length (f) : It is the distance between the pole and centre of curvature (P and f).
7) Power : It is the converging or diverging ability of the mirror.
8) Aperture : It is the effective diameter of the light reflecting area. Intensity of image is directly proportional to the area, which is directly proportional to the square of the aperture.
9) Focal plane : A plane passing from the focus and perpendicular to the principal axis.
The formula of the positions of the object and its image is given by:
${\displaystyle \frac{1}{u}}+{\displaystyle \frac{1}{v}}={\displaystyle \frac{1}{f}}$, where f is the focal length of the mirror.

Difference between a concave mirror and a convex mirror:

Concave mirror	Convex mirror
(1) In a concave mirror, the outer surface of the sphere is reflecting surface	(1) In a convex mirror, the inner surface of the sphere is a reflecting surface.
(2) The radius of curvature of a concave mirror is negative.	(2) The radius of curvature of a convex mirror is positive.
(3) A concave mirror converges all the light rays at a single point.	(3) A convex mirror diverges the light rays falling on it.
(4) A concave mirror may form a real image or a virtual image depending on the position of the image.	(4) A convex mirror always forms a virtual image.

The following diagrams show what happens when rays of light parallel to the principal axis fall on a concave mirror and a convex mirror.
(i) For a concave mirror.

This shows the converging effect of a concave mirror.
(ii) For a convex mirror.

This shows the diverging effect of a convex mirror.

Note: While calculating the positions of the object or its image, all distances are measured from the pole. Distance measured in the direction of incident rays are taken as positive while in the direction opposite of incident rays are taken negative. This sign convection applies to the lens also.