# Sign Convention for spherical Mirror and Mirror Formula class 10 | cbse24

## Sign Convention for Spherical Mirror:

1:-All the distance are measured from pole of the mirror as origin.

2:-Distance measured in the same direction as that of incident light are taken as positive.

3:-Distance measured against the direction of incident light are taken as negative.

4:-Distance measured upward and perpendicular to the principal axis are taken as positive.

5:-Distance measured downward and perpendicular to the principal axis are taken as negative

## Mirror Formula:-

$\frac{1}{Image-distance}+\frac{1}{Object-distance}=\frac{1}{Focal Length}$

$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$

so

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

Where

v=distance of image from mirror

u=distance of object from mirror

f=focal length of the mirror

### Linear Magnification(m):-

The ratio of the height of image to the height of object is known as linear magnification.

$m=\frac{height -of- image}{height- of -object}=\frac{-v}{u}$

$m=\frac{h_{i}}{h_{o}}=\frac{-v}{u}$

Note:

1:-  ho always will be positive

2:- If hi is virtual than it will be positive and hi is real than it will be negative

3:-If the magnification has a minus sign, therefore image is real and inverted.

4:-If the magnification has a positive sign, therefore image is virtual and erect.

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