Try these "busters" to exercise your brain ... they should help you grasp the concepts underlying electromagnetic waves. To gain the maximum effect you should attempt to answer them before looking at the answers!
[1] An electromagnetic wave can be detected using a straight wire or a loop. How do they work?
[2] A radio transmitting antenna, located parallel to the (vertical) y-axis, broadcasts an electromagnetic wave whose electric field oscillates in the y-direction. The wave travels in the x-direction. Three possible wire loops can be used with an LCR resonance circuit - see previous chapter - to detect the wave; one loop lies in the x-y plane, a second in the x-z plane and a third in the y-z plane. Which of these loops will detect the wave, and why?
[3] The intensity of the wave is the average magnitude of the Poynting vector. Both E and B oscillate with the same angular frequency (ω), but what is the frequency of oscillation of the Poynting vector and, hence, the intensity?
[4] The figure below shows the variation of the E vector from a simple antenna at different times.
In what direction is the magnetic field vector, B, in the time interval 0 > t > T/2 and T/2 > t > T?
[5] (Here's an interesting one!) Have you any idea why electromagnetic waves all travel at the same speed - a speed we call the speed of light?
[6] (Be very careful!) Below are two incandescent light bulbs in a circuit:
Bulb (a) is "on" whereas bulb (b) is broken and no longer works. The question is, which one is producing electromagnetic radiation?
[7] Is electromagnetic radiation always produced when charges move? If not, why not?
[8] The two types of astronomy carried out on Earth are "visible" and "radio" astronomy. Why isn't infra-red or x-ray astronomy carried out from Earth?
[9] Earlier, we found that a changing magnetic field (or magnetic flux) produces an emf ... that's Faraday's Law. Since an emf is simply an electric field that causes charges to move (normally in a circuit), we can say that a changing magnetic field produces an electric field. But, is the reverse true ... can a changing electric field produce a magnetic field?
[10] In a previous brain "buster" about electrical charges, we saw that charges cannot exist without an associated electric field. What about the reverse? Can you have an electric field but with no charged objects?
[11] Here's an interesting one! Imagine a charged capacitor with a compass between the plates, as shown below.
There is a wire connecting the two plates via a switch. When the switch is closed a current will flow through the wire (as the capacitor discharges). That momentary current will produce a magnetic field that will be detected by the compass. True or false? Explanations, please!
[12] When an electromagnetic wave is incident normal to a conducting surface, the direction of the E-vector of the reflected wave is reversed. Why is that? What happens to the magnetic field vector, B, on reflection?