Uniform Plane Waves Questions and Answers

Answer: C

In descending order of frequency the sequence is X rays, ultraviolet rays, visible light and UHF waves, which is 2, 1, 3, 4, the third option. X rays have wavelengths of the order of nanometres, ultraviolet rays are longer, visible light lies between about 400 and 700 nm, and UHF waves have wavelengths in the range of centimetres to a metre.

The other options place UHF waves or visible light too high, since radio waves have the lowest frequency of the four.

Answer: D

In a uniform plane wave in free space, both the electric field E and the magnetic field H are transverse, meaning they are perpendicular to the direction of propagation, and they are also perpendicular to each other, which is what makes the wave a transverse electromagnetic (TEM) wave, with the direction of E x H the direction of travel. All three statements are true. The answer is 1, 2 and 3.

Answer: D

Frequency rises from FM radio waves (about 100 MHz) to microwaves (GHz), then visible light (about 10^14 Hz) and X-rays (10^16 to 10^19 Hz). The ascending order is 1, 2, 3, 4. The sequences starting with X-ray or visible light run the wrong way. The wavelengths fall in the same order: FM waves are metres long, microwaves centimetres, visible light about half a micrometre and X-rays fractions of a nanometre, and because the speed of light is constant frequency rises as wavelength falls. The answer is 1, 2, 3, 4.