Question

where should an object be placed before a concave mirror of focal length 20cm so that a real image is formed at a distance of 60cm from it. ​

Answer 1

30 centimetre

between the focus and centre of curvature

its height will be same as it is i.e. m =1

Answer 2

Answer:

u = 30 cm

Explanation:

We have given :

Focal length = 20 cm

Image distance =  60 cm

We have to find object distance .

We know :

1 / f = 1 / v + 1 / u

Since image formed is real :

f = - 20 cm and v = - 60 cm

1 / u = 1 - 3 / 60

u = - 30 cm

Hence object should be place at  distance of 30 cm .