Question

A stationary particle of charge q = 2.2 × 10-8 C is placed in a laser beam (an electromagnetic wave) whose intensity is 2.0 × 103 W/m2. Determine the maximum magnitude of the (a) electric and (b) magnetic forces exerted on the charge. If the charge is moving at a speed of 3.7 × 104 m/s perpendicular to the magnetic field of the electromagnetic wave, find the maximum magnitudes of the (c) electric and (d) magnetic forces exerted on the particle.

Answer 1

I = E^/^2mu_0 c (a) Electric field (E) = squareroot 2 J mu_0 c E = squareroot 2 times 2 times 10^3 times 4 pi times 10^-7 times 3 times 10^8 E = 1.23 times 10^3 v/m Electric force (F) = q = 2.2 times 10^-8 times 1.23 times 10^3 = 2.7 times 10^-5 N (b) Magnetic force on rest charge is zero (c) Force on moving charge F = 2.7 times 10^-5 N same as the charges at rest. (d) Magnetic Force (F) = qvB F_B = 2.2 times 10^-8 times 3.7 times 10^4 times E/c = 2.2 times 10^-8 times 3.7 times 10^4 times 1.23/3 times 10^8 times 10^3 F_B = 3.3 times 10^-9 N