Electromagnetic Waves — Practice

Question 1

A capacitor is charged at 2 A. Find the displacement current between its plates.

Accepted Answer

The displacement current equals the conduction current, so I_d = 2 A.

Question 2

An EM wave has frequency 1e10 Hz. Find its wavelength in air.

Accepted Answer

lambda = c/f = 3e8/1e10 = 0.03 m = 3 cm (microwave region).

Question 3

An EM wave has B0 = 1e-6 T. Find E0 and the average intensity.

Accepted Answer

E0 = c B0 = 3e8 x 1e-6 = 300 V/m. I = c B0^2/(2 mu0) = (3e8 x 1e-12)/(2 x 4 pi e-7) approximately 119.5 W/m^2.

Question 4

Arrange in increasing wavelength: X-rays, visible light, radio waves, IR.

Accepted Answer

X-rays < visible < IR < radio waves (higher frequency means shorter wavelength).

Question 5

A 100 W bulb emits uniformly. Find the intensity at 1 m.

Accepted Answer

I = P/(4 pi r^2) = 100/(4 pi x 1) = 7.96 W/m^2.

Practice — Electromagnetic Waves