EM waves

E(x,t) = E_maxcos(kx - ωt + φ),  B(x,t) = B_maxcos(kx - ωt + φ)
v = λf = ω/k = c  = speed of light = 3*10⁸ m/s
energy carried = proportional to E²

Diffraction and interference

Single Slit, destructive interference:  w sinθ = mλ,  m = 1, 2, …  (w = slit width)

Double slit, grating, constructive interference:  d sinθ = mλ,  m = 0, 1, 2, ….  (d = distance between slits)