In a space lab a 25- sheet of aluminum foil is subjected to a laser beam of intensity on one side and to a beam of intensity on the opposite side,the radiation in each case hitting with normal incidence.What is the net force on the aluminum foil if both sides are considered to be totally reflective?

Question

In a space lab a 25-  sheet of aluminum foil is subjected to a laser beam of intensity  on one side and to a beam of intensity  on the opposite side,the radiation in each case hitting with normal incidence.What is the net force on the aluminum foil if both sides are considered to be totally reflective?

Quizplus · Accepted Answer

When light is incident on a surface, a force known as radiation pressure is exerted on it. The force exerted is equal to the rate of change of momentum of photons being reflected. In this case, the aluminum foil is subjected to two laser beams of equal intensity from opposite sides, and both sides are considered totally reflective.

The net force on the foil will be the difference between the forces exerted by the two beams. As the two beams have the same intensity, the momenta imparted to the foil will also be the same, but in opposite directions. Therefore, the net force on the foil will be zero, and the sheet will remain stationary.

However, if we consider the radiation pressure in terms of energy density (power per unit area), we get P/c, where P is the power of the beam and c is the speed of light. Therefore, the force per unit area is proportional to the intensity of the beam. In this case, the net force on the foil will be zero, as the intensities of the beams are equal.

Therefore, the correct answer is B.

In a Space Lab a 25- Sheet of Aluminum