What is the sign of focal length of convex mirror? (JEE Mains 2021- 24 Feb 2021 Shift 1)

A. +ve

B. -ve

C. Can be +ve or -ve

D. None of these

Solution: A

As per cartesian sign conventions, the focal length of a convex mirror is positive as the image is formed behind the mirror. 

Cartesian sign conventions: 

1) Light initially propagates from left to right. All signs are taken from the pole of the mirror i.e. origin point. Sign is taken as negative in front of a spherical mirror and positive behind the spherical mirror. 

2) If the image is formed behind the mirror, sign will be positive. 

3) If the height is measured above the principal axis it will be positive and if measured below the axis, the sign will be negative. 

Hence, option (A) is correct.

You can also study other topics of Physics like Units and Measurements, Newton's laws of Motion, Light, Force and Pressure, etc. 


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