Question

suppose the distance from the candle to the lens is 40 cm, and the distance from the lens to the screen is also 40 cm. What is the focal length of the lens?

Answer 1

Step-by-step explanation:

The image is formed on a screen therefore image must be real and lens must be convex.

So it must have been formed on the other side of the lens.

U, object distance = - 40 cm ;

V, image distance = 40 cm ;

Len formula

`(1)/(v) -(1)/(u) =(1)/(f)`

Putting the given values

`(1)/(40) +(1)/(40) =(1)/(f)`

`(2)/(40) =(1)/(f)`

f = 20 cm .