Question

An object is placed at a distance of 100 cm from a converging lens of focal length 40 cm.
(i) What is the nature of image?
(ii) What is the position of image?

Answer 1

Given:
Object distance, u = $-$100 cm
Focal length, f = 40 cm
Applying lens formula, we get:
1/v $-$1/u = 1/f
1/v $-$ 1/($-$100) = 1/40
or, 1/v = 1/40 - 1/100
or, 1/v = 6/400
or, 1/v = 3/200
or, v = 200/3 = +66.6 cm
Now
Magnification, m = v/u
m= (200/3)/($-$100)
m= $-$2/3
(i) The value of magnification is negative, therefore, the image will be real and inverted.
(ii) The value of v is (+66.6 cm); therefore, the image is formed 66.6 cm behind the convex lens.