Question

The famous Russian physicist P. N. Lebedev, in his experiments, directly established that light exerts a force on a body absorbing the light and that the numerical value of this force is equal to the entire energy of light arriving in one second divided by the velocity of light (all quantities are measured in c.g. units). What is the force exerted by the rays of the sun on the earth if they are entirely absorbed by the surface of the earth? When they strike the surface of the earth normally, the sun' rays transfer an energy of 1.94 cal to every square centimetre of surface in one minute. The earth' radius is 6400 km.

Answer 1

Explanation:

Falling on the Earth' surface is the entire light energy travelling from the Sun inside the solid angle determined by a circle equal in area to the cross section of the Earth. The total energy absorbed by the Earth is E = πR2 x 1.9 cal, where R = 6400 km is the radius of the Earth. The force exerted by the solar rays on the Earth, when they are completely absorbed by the Earth' surface is F = E/c.