Question

An object of height 1.2 cm is placed before a concave mirror of focal length 20cm so that a real image is formed at a distance of 60cm find the position of object what is a height of a image formed

Answer 1

hey!!
Given mirror is concave mirror
Thus
f = -20 cm
u = ?
v = -60
h = 1.2 cm
Now we have to find the nature of image , position of object and size of image

Thus using mirror equation
1/f = 1/u + 1/v
=> 1/v = 1/f-1/u
=>1/u = -1/20+1/60
=> 1/u = -2/60
=> 1/u = -1/30
=> u = -30 cm { hence image will be formed beyond c

Now magnification
m = -(v/u) = (h'/h)
m = -(-30/-15)
= -2 { it means that the image will be real , inverted and magnified
Now again
m = h'/h

2 = h'/1.2
=> h' = 2.4cm
hence the size of image will be 2.4cm

Answer 2

Height of the object (h) : 1.2cm

Focal length (f) : -20cm

Distance of image (v) :60cm

1/v +1/u =1/f

1/60 +1/u =1/-20

1/u =-1/20+1/60

1/u= -3+1/60

1/u=-2/60

1/u=-1/30

u= -30

Magnification = h'/h =-v/u

=h'/1.2= -(-60)/-30

=h'/1.2 =-2

=h' =-2*1.2

= h' =2.4 cm