Question

An object 5 cm high is placed at a distance of 60 cm in front of a concave mirror of focal length 10 cm. Find (i) the position and (ii) size, of the image.

Answer 1

Object distance , u= -60cm

Focal lenght , f =-10cm

Object size = 5 cm

v =?

Mirror formula,

1/v + 1/u = 1/f

1/v = 1/u - 1/f

1/v= 1/-(60) +1/-(10)

1/v = (-1+6)/60

1/v = (-5)/60

1/v = -1/12

v = -12

Image position = -12

Size of the image,

Magnification , m= -v/u

m = -(-12)/(-60)

m = 12/(-60)

m = 1/-5

m= -0.2

Then ,

m = h'/h

-0.2= h'/5

-0.2 × 5 = h'

h' = -1

(i) the position:12cm in front of the mirror

(ii) size of the image: 1cm