Class 10 CBSE Physics Chapter:LIght. Sign Conventions for Spherical Mirrors (Concave & Convex)

The New Cartesian Sign Convention is used for mirrors. The conventions are:

1. All distances are measured from the pole (P) of the mirror.

2. Distances measured in the direction of incident light (right side) are positive (+), while distances measured opposite to the direction of incident light (left side) are negative (-).

3. Distances above the principal axis (upright/positive y-axis) are positive (+), and distances below the principal axis (inverted/negative y-axis) are negative (-).

Sign Conventions for Different Parameters:

Parameter	Concave Mirror	Convex Mirror
Focal Length (f)	Negative (-) (Focus on left)	Positive (+) (Focus on right)
Object Distance (u)	Always Negative (-) (Object placed in front)	Always Negative (-) (Object placed in front)
Image Distance (v)	Negative (-) for Real images (Left side)  Positive (+) for Virtual images (Behind mirror)	Always Positive (+) (Image always behind the mirror)
Image Height (h')	Negative (-) for Inverted images   Positive (+) for Upright images	Always Positive (+) for Upright images
Magnification (m = h'/h)	Negative (-) for Real & Inverted images   Positive (+) for Virtual & Upright images	Always Positive (+) for Virtual & Upright images

Key Points to Remember:

• Concave Mirrors can form both real (inverted) and virtual (upright) images, so v and h' can be positive or negative.

• Convex Mirrors always form virtual and upright images, so v and h' are always positive.

• Magnification (m) is negative for real, inverted images and positive for virtual, upright images.