Question

a object of height 1.2is placed before a concave mirror of focal length 20 cm so that a real image is formed at a distance of 60cm from it find tha position of an object.what will be the height of the image formed

Answer 1

Heya,

According to the question,

Height of objects(h) = 1.2 cm

Focal length of concave mirror (f) = -20cm

Image distance (v) = 60cm

Object distance (u) = ?

Height of image (h1) = ?

Mirror formula ;

1/u + 1/v = 1/f
1/u = 1/f - 1/v
1/u = -1/20 - 1/60
1/u = (-3 - 1)/60
u = -60/4
u = -15

So, object distance (u) = -15cm

Magnification of mirror:

h1/h = v/u
h1 = hv/u
h1 = 1.2×60/-15
h1 = -1.2×4
h1 = -4.8

So, image height(h1) = -4.8cm

Hope this helps....:)

Answer 2

1/f = 1/v + 1/u
1/u = -1/20 - 1/60
1/u = -3-1/60
1/u = -4/60
U = -15cm
So the position of the object will be at f (focus).
Hi/ho = -v/u
Hi/1.2 = 60/-15
Hi = 1.2 x -4 Therefore, hi = -4.8cm Hope it helps ,