A point source of light is placed at distance of 2f from the converging lens of focal length f.the intensity on the other side of the lens is maximum at a distance 1.f 2.2f?

using the equatin for for lens:

 

object distance, u = -2f

focal length, F = +f

let the image distance be v

the equation is:

 

1/v - 1/u = 1/f

1/v = 1/(2f)

thus the image will form at 2f and thus the intensity will be maximum at 2f