I have a question regarding diffraction. The actual question itself isn't too hard (I don't think!), but I'm having problems with the wording of it. Basically it says that a lens of focal length xcm is placed behind the slit, and the screen where the diffraction pattern is formed is in the focal plane of the lens. Now does behind the screen mean that a) the lens is between the light source and slit, or b) between the slit and screen? I'm pretty sure I have the knowledge required to answer either version of the question, but obviously don't want to answer the wrong one. Which version would you guys assume it is? I think its possibly a).