To know the sign for Concave and Convex mirror when they give some problems to do, we must know the formation of images by Concave and Convex mirror.

Concave mirror forms real and inverted image at the left side of the mirror. Because, in Concave mirror, the rays meets at a point, means, rays will converge at a point. So, distance and focal length will be taken as negative (-ve).

[Note:- In Concave mirror, reflecting surface is curved inwards, so image forms left side of the mirror.]

Convex mirror forms virtual and erect image at right side of the mirror. Because, in Convex mirror, the rays starts to diverge, means, rays starts to go far from the Convex mirror when the rays strike the Convex mirror. So, distance and focal length will be taken as positive (+ve).

[Note:- In Convex mirror, reflecting surface is curved outwards, so image forms at right side of the mirror.]

When you come for the magnification for the Concave and Convex mirror, the magnification formula will be
(-v/u) as the mirror formula sign is in positive. i.e.
(1/v + 1/u = 1/f).


[Note - 1:- If the magnification value is positive and less than the value 1, the image is virtual and smaller in size.].

[Note - 2:- If the magnification value is negative and more than the value 1, the image is real and bigger in size].

Concave and convex mirrors are two types of mirrors that are used in optics. They have different properties and are used for different purposes. In order to solve problems related to these mirrors, it is important to understand their properties and how to find their focal length, magnification, and other parameters. One important step in solving these problems is to find the sign for concave and convex mirror problems.


In optics, a sign convention is used to determine the sign of various parameters. The sign convention for concave and convex mirrors is as follows:

• The distance of the object from the mirror is positive if the object is in front of the mirror, and negative if the object is behind the mirror.


• The distance of the image from the mirror is positive if the image is in front of the mirror, and negative if the image is behind the mirror.


• The radius of curvature of the mirror is positive for a concave mirror and negative for a convex mirror.


• The focal length of the mirror is positive for a concave mirror and negative for a convex mirror.


• The magnification of the mirror is positive for an upright image and negative for an inverted image.

Let's consider two examples to illustrate how to find the sign for concave and convex mirror problems.

Example 1: A concave mirror has a radius of curvature of 20 cm. An object is placed 30 cm in front of the mirror. Find the focal length of the mirror.

• The radius of curvature of the concave mirror is positive (+20 cm).


• The distance of the object from the mirror is positive (+30 cm).


• The focal length of the mirror can be found using the formula: 1/f = 1/do + 1/di, where do is the distance of the object from the mirror and di is the distance of the image from the mirror.


• Since the mirror is concave, the focal length is positive.

Therefore, the sign of the focal length is positive.

Example 2: A convex mirror has a radius of curvature of 30 cm. An object is placed 40 cm in front of the mirror. Find the magnification of the mirror.

• The radius of curvature of the convex mirror is negative (-30 cm).


• The distance of the object from the mirror is positive (+40 cm).


• The magnification of the mirror can be found using the formula: m = -di/do, where di is the distance of the image from the mirror and do is the distance of the object from the mirror.


• Since the mirror is convex, the magnification is negative for an upright image.

Therefore, the sign of the magnification is negative.


In conclusion, the sign for concave and convex mirror problems is determined using a sign convention. This convention helps in finding the sign of various parameters such as the distance of the object from the mirror, the distance of the image from the mirror, the radius of curvature of the mirror, the focal length