# How do I calculate the intensity of a diffraction pattern in a double slit experiment?

I'm currently struggling to understand the physics behind this question (purely because our lecture hasn't given us proper grounding in quantum mechanics). In a double slit experiment, you are given $\psi_1= A_1e^{-i(ky-wt)/\sqrt{1+y^2}}$ and $\psi_2 = A_2e^{-i(ky+\pi y-wt)/\sqrt{1+y^2}}$ where $A_1$ and $A_2$ are normalization constants to be determined. These state vectors represent the diffraction pattern that occurs at 2 separate vertical detectors as a light source hits a screen.

I'm asked to calculate intensity when: a) 2 slits are opened and a light source is used to detect which slit the electron goes through. b) 2 slits are open with no light source.

I found $A_1$ and $A_2$ to both equal $1/\pi$ and to get intensity I know I have to superposition them and square the sum so intensity = $\psi_1^2 + \psi_2^2+2\psi_1\psi_2$. However I don't know what it means by the options a) and b) or if I am to get a single value for the intensity or is it to be in respect of $y$ and $t$. I would really appreciate it if someone could take the time to explain to me what it is I am meant to do.

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Check if I formatted correctly the equations. – Ignacio Vergara Kausel Oct 20 '13 at 1:13
I would read the cases (a) and (b) again very carefully and think about what you're instructor has told you about QM. Draw it out on a piece of paper and go step by step. What is meaningful here? What did my lecturer say again? I think it is important for you to figure it out. – Derek E Oct 20 '13 at 2:27