Question

list four characteristics of the image formed by a convex lens of focal length 20 cm when the object is placed in front of it at a distance of 10 cm from its optical centre

Answer 1

1.virtual image

2.erect image

3.enlarged image

4.on same side of lens as of object(left)

Answer 2

focal length of convex lens, f = +20cm

object distance, u = -10cm

use lens maker formula,

1/v - 1/u = 1/f

or, 1/v - 1/-10 = 1/20

or, 1/v = 1/20 + 1/-10

or, 1/v = -1/20 => v = -20

here it is clearly shown that, image is formed at the same side of lens 20cm from the pole of lens.

magnification, m = v/u = -20/-10 = 2,

magnification is greater than 1, so size of image is greater than size of object.

magnification is positive so, image is virtual and erect

so, four characteristics of image :

1. image is virtual

2. image is erect.

3. image is enlarged

4. image is formed at the same side of lens.