Question

An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. [All India]

Answer 1

Given-

h₁=50cm

h₂=20cm

v=10cm

To Find-

focal length  (f)

sol-

m=h₁/h₂=v/u   (Magnification)

we get,

u=vh₁/h₂

=10*50/-20

u=(-25cm)

now,

1/v-1/u=1/f   (Lens Formula)

=1/10-1/(-25)

LCM=250

=25+10/250

=250/35

f= 7.14cm

Hence the focal length is 7.14cm

Answer 2

hi friends

here is your answer