Question

a 6 cm tall object is placed perpendicular to the principal axis of a concave mirror of focal length 30cm. the distance of the object from the mirror is 45cm. use mirror formula to determine the position, nature and size of the image formed.

Answer 1

This is the Question of CBSE class 10 (2018-19).

Answer 2

In this question we will apply the mirror formula.

Given the object distance, The image distance and the focal length ,the mirror formula is given as :

1/f = 1/u + 1/v where :

f = the focal length

u = the image distance

v = the object distance

In this case :

f = 30 cm

v = 45 cm

Since the image distance is not given we can get the image distance.

1/u = 1/f - 1/v

= 1/30  -  1/45 =  1/90

Therefore u = 90 cm

Magnification = Image distance/object distance

Magnification = 90/45 = 2

Magnification = image height / object height.

By substitution :

2 = h/6

h(image height) = 6 × 2 = 12 cm

The characteristics of the image formed are as follows:

Nature: It is real image and larger than the object.

Position : 90cm

Size : 12 cm