Question

A plate of mass 10 gm is in equilibrium in air due to the force exerted by light beam on plate. Calculate power of the beam. Assume plate is perfectly absorbing.

• A. $3\times {10}^{7}W$
• B. $2\times {10}^{7}W$
• C. $3\times {10}^{5}W$
• D. $2\times {10}^{5}W$

Answer 1

The correct option is A $3\times {10}^{7}W$

$F_{photon}=F_{gravity}\frac{p}{c}=Mgp=3\times {10}^8\times {10}^{-2}\times 10p=3\times {10}^{7}W$