Question

find the magnification of the convex lens object of height 9cms and the image height is 36cms​

Answer 1

Answer:

Magnification of image is, ∣m∣=2 as image size (h

′

) is double the object size (h)

Thus, m=±2

as for a less, m=

u

v

(object distance =u , image distance =v)

⇒

u

v

=±2 ⇒v=2u or v=−2u

(i) case I : v=2u⇒u=v/2 then by lens formula,

v

1

−

u

1

=

f

1

⇒

v

1

−

v

2

=

20

1

⇒v=−20 cm

(ii) case II : when v=−2u⇒u=−v/2, so

v

1

−

u

1

=

f

1

⇒

v

1

+

v

2

=

20

1

⇒v=20/3 cm

∴ Image distance can be 20 cm (if image is virtual) on can be 20/3 cm (if image is real)