2. Constructive and destructive Interference 2丌 2丌 S: E= E10 cos(at+Pio )=E1o cos(at+pu 2丌 2丌 S2:E2=E20C0s(0+20 cos(at + p20 n,n 2丌 △p=(n20-10)-n,(nh272-nf) 士2k元 constructive k=0.1 ±(2k+1)z destructive( ) 2 ( ) 2 2 1 1 0 20 10  = − − n r − n r      destructive constructiv e k k k 0,1... (2 1) 2 =     +   =    2. Constructive and Destructive Interference ) 2 ) cos( 2 : cos( 1 1 0 1 1 0 1 0 1 1 1 1 0 1 0 S E E t r E t n r       =  +  − = + − ) 2 ) cos( 2 : cos( 2 2 0 2 2 0 2 2 2 2 0 2 0 S E E t r t n r       =  +  − = + −