question_answer 17)

    Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 minutes is (a) 36 x10-5 Kg m/s          (b) 36 x 10-4 Kg m/s ( b) 108 x104 Kg m/s        (d) 1.08 x 1O7-Kg m/s

Answer:

  (b) Here, energy flux,  W/cm2;  Area, A = 30 cm2 ; time t = 30 min = 30 x 60 s Total energy falling on the surface in time t is, Momentum of the incident light = Momentum of the reflected light =0                Momentum delivered to the surface kg m/s.