pic】 FIG.3:Electromagnetic Wave Propagation. Scalar wave,Amplitude-A→？ Intensity-A2? Early attempt:Intensitymaterial density,particle mass distributed in wave.But wave is endless in space,how can it fit the idea of a particle which is local. B.Wave packet-a possible way out? particle=wave packet-rain drop -an endless train,How can it be connected with particle picture? Two examples of localized wave packets .Superposition of waves with wave number between (ko-Ak)and (ko+k)-square packet A,k0-△k<k<k0+△k P()= 0, elsewhere (x)= V交o)ek rk知+△k Aeikrdk 2Am(△keh V2 Amplitude 9FIG. 3: Electromagnetic Wave Propagation. Scalar wave, Amplitude - A →? Intensity - A 2 →? Early attempt: Intensity → material density, particle mass distributed in wave. But wave is endless in space, how can it fit the idea of a particle which is local. B. Wave packet - a possible way out? particle = wave packet - rain drop e ik0x− an endless train, How can it be connected with particle picture? Two examples of localized wave packets • Superposition of waves with wave number between (k0 − ∆k) and (k0 + ∆k) - square packet ϕ(k) =    A, k0 − ∆k < k < k0 + ∆k 0, elsewhere ψ(x) = 1 √ 2π Z ϕ(k)e ikxdk = 1 √ 2π Z k0+∆k k0−∆k Aeikxdk = 1 √ 2π 2A sin (∆kx) x | {z } Amplitude e ik0x 9