Question

A convex lens of power +4D is placed at a distance of 40cm from a screen.At what distance from the lens should a candle placed, so that the image is formed on the screen?

Answer 1

Hey frnd hope this helps u..

Given power of. convex ok lens={1/f}=4

hence focal length (f)=0.25 meter

f=0.25 * 100 = 25cm

now image distance (v)=40cm
(screen is at 40 cm)

hence using lens formula .(1/f)=(1/v)-(1/u)
where u =object distance

hence putting all value

(1/25)= (1/40) - (1/u)

hence( 1/u) = (1/40) - (1/25)

(1/u). =(5-8) /200

u(object distance) = (-200/3) cm

where -ve sign indicates the object is left side of the lens..