An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of the object on a screen placed at a distance 75 cm from the lens. Find :
1) the focal length of lens
2) the magnification.

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Solution

v=75cm(+ve)

u=100-75
=25cm(-ve)
By lens formula
1/f=1/v-1/u
=1/75-1/(-25)
=(1+3)/75
=4/75
So, f=75/4
=18.75cm
(b) m=v/u
=75/(-25)
=-3

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An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of the object on a screen placed at a distance 75 cm from the lens. Find : 1) the focal length of lens 2) the magnification.

v=75cm(+ve) u=100-75 =25cm(-ve) By lens formula 1/f=1/v-1/u =1/75-1/(-25) =(1+3)/75 =4/75 So, f=75/4 =18.75cm (b) m=v/u =75/(-25) =-3

An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of the object on a screen placed at a distance 75 cm from the lens. Find :
1) the focal length of lens
2) the magnification.

v=75cm(+ve)

u=100-75
=25cm(-ve)
By lens formula
1/f=1/v-1/u
=1/75-1/(-25)
=(1+3)/75
=4/75
So, f=75/4
=18.75cm
(b) m=v/u
=75/(-25)
=-3