Question

a needle is placed 50 cm from the lence forms an image on a sreeen placed 90 cm on either side of the lens determine the focal lengthof convex lens

Answer 1

using formula of lens formula

Answer 2

u= -50 cm

v= 90 cm (since image is formed on screen of convex lens so it is real)

by lens formula

1/f = 1/v - 1/u

= 1/90 -( 1/-50)

= 1/90+ 1/50

= (50+90)/90×50

= 0.031

so, f= 1/0.031 cm

= 32.2 cm

@skb