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
Given
Magnitude of energy flux of light ϕ= 20 W/cm2
Explanation:
The energy provided by the light on the surface in one second is obtained as:
ϕA
The total energy absorbed by the surface in 30 minutes or 30x60=1800 seconds is therefore,
We know that for quanta of light the energy E and momentum p are related as:
Where c is the speed of light in the medium. Assuming the medium to be vacuum in this case we have c = 3 x 108 m/s , therefore the momentum,
1