We use our detector to measure the diffraction pattern similar to the one for photons labeledP 12
below. If wecover up slit 2we get the distribution labeledP 1 and if we /emphtextcover up slit 1
we get the intensity distribution labeledP 2. We could have done the same with our photons above.
Now we will try to see which slit each electron passes through. We putabright light source near
the slitsand detect light bouncing off the electron so we can see which slit it passes through.