Question

3. An object is placed perpendicular to the principal axis of a convex lens
of focal length 20 cm. The distance of the object from the lens is 30 cm.
Find (i) the position (ii) the magnification and (iii) the nature of the image
formed.

Answer 1

Answer:

1 .60cm

2.2

3.real and inverted

Answer 2

Solution :-

As per the given data ,

• Focal length = + 20 cm

[ Focal length of a convex lens is always positive ]

• Object length = - 30 cm

[ Distances are always measured from the pole of the mirror ]

As per the lens formula ,

1 / f = 1/ v - 1 / u

here ,

• f = focal length
• v = image distance
• u = object distance

→ 1 / 20 = 1 / v + 1 / 30

→ 1 / v = 1 / 20 - 1/ 30

→ 1 / v = 3 - 2 / 60

→ 1 / v = 1 / 60

→ v = 60 cm

The image is formed at a distance of 60 cm on the other side of the lens .

Magnification ,

→ m = v / u

→ m = 60 / - 30

→ m = - 2

Here , negative sign denote that the image formed is real and inverted

As the value of magnification is 2 , the image formed is magnified