Radiation of intensity I is normally incident on an object that absorbs a fraction f of it and reflects the rest. We have to find the radiation pressure.
|
Solution: Click For PDF Version Let us consider a unit area of the object on which radiation of intensity I is normally incident. It is given that the object absorbs a fraction f of it and reflects the rest. Pressure on the object due to the fraction of the radiation that is absorbed will be equal to the momentum transferred to the object.
The fraction
of the radiation that is reflected will be
which will be the additional pressure on the object. Therefore, the total pressure on the object due to radiation will be
|
.
and therefore the momentum transferred per unit time on a unit area
of the object because of reflection of the radiation will be
,