it is zero (destructive interference!), again in agreement with observation. At the exactly intermediate points we have w = iz or w = – iz (so that cos θ = 0) whence |w + z |2 = |w ± iw |2 = |w|2 + |w |2 = 2|w|2 giving twice the intensity as for just one slit (which would be the case for classical particles). We shall see at the end of the next section how to calculate where the bright, dark, and intermediate places actually are.
