Question

a concave mirror of focal length 20cm forms a real image at a distance of 40 find the position of object

Answer 1

Given, 1/f=-1/40 cm

Let the distance from the mirror to the object be x cm .

So, 1/v=1/4x

According to mirror formula,

1/v+1/u=1/f

1/x+1/4x=1/40

On solving we get,5/4x=1/40

So,x=(5×40)/4=50 cm

So,the object is 50 cm in front of the mirror....
HOPE IT WILL HELP YOU

Answer 2

Answer:

Explanation:

Image distance, v = -40cm

Focal length, f = -20cm

Object distance, u = ?

We know that,

1/u + 1/v = 1/f

=> 1/u = 1/f - 1/v

=> 1/u = 1/-20 - (1/-40)

=> 1/u = -1/20 + 1/40

=> 1/u = -2/40 + 1/40

=> 1/u = -1/40

=> u = -40 cm