Question

A concave mirror of focal length 20cm is placed at a distance of 5cm on a wall. Calculate distance of object in order to obtain it's real image on the wall

Answer 1

Since it is a concave mirror therefore the focal length is -20 and image distance is -50 therefore the object distance will be -33.3 cm

Answer 2

F = - 20cm {concave mirror}

U = -5cm , v= ?

Mirror formula : 1/f = 1/u + 1/v

1/-20 = 1/-5 + 1/v

1/v. = 1/-20 - 1/-5

1/v = 1/-20 + 1/5

1/v = 1/20- 1/5

Taking LCM

1/v = -3/20

Therefore , v = -20/3 cm

Or , v = - 6.66 cm

Regards,