//chapter 2
//Pavg=0.5*|E|^2/etta0,Prmax=2*10^-6W,Aem=Prmax/Pavg
printf("\n");
E=50*10^-3;
Etta0=120*(%pi);
printf("the electric field is %eV/m",E);
Pavg=0.5*(50*10^-3)^2/(120*(%pi));
printf("\nthe average power is %gW",Pavg);
Aem=(2*10^-6)/(3.315*10^-6);
printf("\nthe maximum effective aperture area is %gm^2",Aem);