question_answer 46)

    A plane EM wave travelling along z direction is described by                 (i) The average energy density of the wawve is given by (ii) The time averaged intensity of the wave is given by  

Answer:

                  (i) The electromagnetic wave carry energy which is due to electric field vector and magnetic field vector. In electromagnetic wave E and B vary from point to  point and from moment to moment. Let E and B be their time averages. The energy density due to electric field E is                                 The energy density due to magnetic field B is                                   Total average energy density of em wave                                  ?(i) Let the em wave be propagating along z-direction. The electric field vector and magnetic field vectors be represented by                                 The time average value of E2 over complete cycle . and time average value ofB2 over complete cycle =.                                 (ii) we know that and                                                       Hence,                  Time average intensity of the wave