Question

A small source radiates an electromagnetic wave with a single frequency into vacuum, equally in all directions. As the wave moves, determine what happens to each of the following.
(a) frequency increases decreases remains constant
(b) wavelength increases decreases remains constant
(c) speed increases decreases remains constant
(d) intensity increases decreases remains constant
(e) amplitude of its electric field increases decreases remains constant

Answer 1

Answer:

a) Frequency remains constant

b) Wavelength remains constant

c) speed of the wave remains constant

d) Intensity decreases

e)  amplitude of its electric field decreases

Explanation:

a)  Frequency can be defined as the number of crests that pass a fixed point in the medium in unit time. It is the source of the wave that will determine the frequency. If the small source is changed to a bigger and faster one then the frequency will change. In our case, there is no change of source of wave, so the frequency remains constant.

b) The speed of of the wave is directly proportional to the wavelength. If we double the speed, the wavelength also doubles. Since the speed has not been doubled in our case, the wavelength will remain constant.

c) As indicated in b) since the wavelength is proportional to speed and it has not changed in our case, then the speed remains constant.

d) The intensity of a wave decreases as it moves further away from the source.

e) The intensity is related to the amplitude. Since the intensity decreases, the amplitude also decreases.