AP(t=2APm cos(amt)sin( @,t) A beat--that is, a maximum intensity-occurs whenever cos(Oamnt) equals +1 or-1, since the intensity depends on the square of the amplitude. Each of these values occurs once in each cycle of the envelope, thus 2 beat amp 2(19-36A beat--- that is, a maximum intensity—occurs, whenever equals +1 or -1 ,since the intensity depends on the square of the amplitude. Each of these values occurs once in each cycle of the envelope, thus (19-36) cos( t) amp beat = 2amp = 1 −2 P(t) 2 P cos( t)sin( t)  =  m amp a v