A continuous laser delivers of light in a narrow beam that strikes a perfectly…

PHYSICS · Multi-part · Fermi University Physics · Mechanics & Dynamical Systems · Relativity & Gravitation · Momentum, energy and conservation laws

Relativity and Gravitation, Ch Relativistic momentum, energy and collisions

Problem

A continuous laser delivers

P = 1.0\ \mathrm{MW}

of light in a narrow beam that strikes a perfectly reflecting flat mirror at normal incidence, so that each photon's momentum is reversed in direction and unchanged in magnitude. Take the photons to be all of the same energy,

1.2\ \mathrm{eV}

, with

1\ \mathrm{eV} = 1.602\times10^{-19}\ \mathrm{J}

. Ignore any absorption and any motion of the mirror. ((a)) Estimate the number of photons striking the mirror per second. ((b)) Estimate the force the beam exerts on the mirror, in N.

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