Question

a beam of light converges towards a point o behind a convex mirror of focal length 20 cm calculate the position of image if the point o is 10cm behind the mirror

Answer 1

f = -20 cm

u = -10 cm

1/f = 1/u + 1/v

-1/20 = -1/10 + 1/v

= 1/v = 1/20

v = 20 cm

Answer 2

Answer:

The position of the image is -20cm.

Explanation:

Given: focal length = 20cm

object position = $u$ = 10cm

Mirror formula :  $\frac{1}{v} +\frac{1}{u} =\frac{1}{f}$

where,

$v$ is the distance of the image from the pole,

$u$ is the distance of the object from the pole,

$f$ is the focal length of the lens.

Putting the given values into the mirror formula given above, we get,

$\implies \frac{1}{v} +\frac{1}{10} =\frac{1}{20}$

Rearranging the equation,

$\implies \frac{1}{v} =\frac{1}{20}-\frac{1}{10}$

$\implies \frac{1}{v} =\frac{2-1}{20}$

$\implies \frac{1}{v} =-\frac{1}{20}$

$\implies v=-20 cm$

Position of image is -20cm.

The negative sign indicates that the image is formed on the left side of the lens which is the same side of lens where object is kept.

Also, the image formed will be virtual.

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