In an evacuated chamber a thin flat disc of diameter and mass is held motionless

PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Electromagnetic waves and their propagation · Electromagnetic waves and their propagation

Electricity, Magnetism and Electromagnetism, Ch Plane electromagnetic waves: polarisation, energy flux and radiation pressure

Problem

In an evacuated chamber a thin flat disc of diameter

0.20\,\mathrm{mm}

and mass

1.0\times10^{-9}\,\mathrm{kg}

is held motionless, horizontal, by a vertical laser beam shining up at it. Take the disc to be a perfect reflector, the beam to strike it at normal incidence with uniform intensity and to cover the disc exactly (none of the light misses it), and the beam to be a plane wave at the disc. There is no air, and

g = 9.81\,\mathrm{m\,s^{-2}}

. ((a)) What power must the beam carry? ((b)) What is the intensity of the beam at the disc? ((c)) Find the amplitudes

E_0

and

B_0

of the wave's electric and magnetic fields at the disc.

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