Show that the radiation pressure exerted by an EM wave of intensity I on a surface kept in vacuum is `I//c`.

Explanation

Pressure `P=("force")/("area")=F/A=1/A(DeltaP//Deltat)xxc/c [ :' F=(Deltap)/(Deltat)`=rate of change of momentum]
`:. P=1/(Ac Deltat)xxcDeltap=1/(Ac Deltat)xxDeltaU`.....(i)
(where `c Deltap=DeltaU=` energy imparted by wave in time `Deltat`)
Intensity, `I=("energy imparted")/("areaxxtime") =(DeltaU)/(ADeltat)=Pc` [form(i)]
`:. P=I//c`