Question

calculate the focal length of concave mirror when an object placed at a distance of 40cm makes an image equal to the size of object

Answer 1

-40 cm

Explanation:

given size of the object = size of the image then th formulae =

(1/1) = -(v/u)

(1/1)= -(v/40)

ans : v= -40cn

Answer 2

Answer:

focal length of concave mirror is -8cm

Explanation:

focal length = ?

u = - 40 cm

m = h'/h = v/u

1/4 = - v/40

v = - 10cm

1/v + 1/u = 1/f

1/-10 +1/-40 = 1/f

1/-8 = 1/f

f = - 8cm