Question

a 20cm tall object is placed perpendicular to the principle axis of a convex lens of focal length 10cm the distance of the object from the lens is 15cm. Find the nature, position,and size of the image.Also find its magnification.

Answer 1

In the other answer , the formula used to find height of image is wrong

here is the correct steps

Answer 2

Explanation:

Height of the object (h) : 20 cm

Focal length of convex lens (f) : 10 cm

Distance between the object (u) : -15 cm

To find :

i) Distance between the image (v)

(ii) Magnification (m)

(iii) Height of the image (h')

i) By using lens formula

1 - 1 = 1

v u f

1 - (- 1 ) = 1

v 15 10

1 + 1 = 1

v 15 10

1 = 1 - 1

v 10 15

1 = 3- 2

v 30

1 = 1

v 30

v = 30cm

Thus the image is formed at 30 cm on other side (i.e right side ) of the lens.

ii) Magnification in terms of u and v:

m = v

u

m = 30

-15

m = -2

iii) Determination of magnification:

m = h'

h

-2 = h'

20

By cross multiplication,

h' = -2 × 20

h' = -40cm

So, a real and inverted image of large size is formed.

Ans