# Reflection of Light Part-2

Use of Concave Mirror:

Use of Convex Mirror:

Sign Convention for Reflection by Spherical Mirrors

The conventions are as follows –

(i) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.

(ii) All distances parallel to the principal axis are measured from the pole of the mirror.

(iii) All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.

(iv) Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive.

(v) Distances measured perpendicular to and below the principal axis (along –y-axis) are taken as negative.

Mirror Formula and Magnification:

## Mirror Formula

Now, that all these conventions are clear; let us know move on the mirror formula. Mirror Formula helps us to find:

• Image distance which is represented as ‘v’.
• Object distance which is represented as ‘u’.
•  Focal length which is represented as ‘f’.

And is written as:

Magnification

It is represented as the ratio of the height of the image to the ratio of the height of the object. Magnification is denoted as the letter ‘m’. Where,

Magnification (m) = h/h’

h’ is the image height

h is the object height

Magnification can also be related to the image distance and object distance; therefore it can also be written as:

m = -v/u

Where v is the image distance and u is the object distance.

Hence, the expression for magnification (m) becomes: