Question

Fill in the blanks: The equation of mirror formula is _______ .

Answer 1

Hint:In physics, generally we use spherical mirrors and especially concave spherical mirror which is a converging mirror and other one is convex mirror which is a diverging mirror which means when light rays falls on reflecting surface of mirror rays gets converged and diverged.

Complete answer:
Firstly we must understand the sign conventions and various parameters which define the mirror formula. Mirror formula is given as,
${\displaystyle \frac{1}{f}}={\displaystyle \frac{1}{v}}+{\displaystyle \frac{1}{u}}$
Here, $f$ is denoted for focal length which is the distance between pole and focus of a concave or convex mirror. $v$ Is denoted for image distance which is measured from pole to the point where image of an object is formed. $u$ Is denoted for object distance which is measured as from pole to the point where the object is placed.

Sign convention: The distances are always measured from the pole of mirrors.Distances measured in the direction of incident ray are taken as positive and the distances measured along the direction opposite of incident ray is always taken as negative.Let us take a simple example of concave mirror to understand this

Here image distance measured from pole $P$ is in the direction of incident ray hence will be taken as positive but focal length and object distance will be taken as positive.

Hence, the equation of mirror formula is ${\displaystyle \frac{1}{f}}={\displaystyle \frac{1}{v}}+{\displaystyle \frac{1}{u}}$.

Note:The reflecting part of the concave spherical mirror is that which caves inwards and the reflecting part of convex spherical mirror is one which caves outwards. In convex mirror focal length $f$ is positive and object distance $u$ is taken as negative.