PHYS102: Introduction to Electromagnetism

Electromagnetic waves satisfy the superposition principle, and therefore it is possible for any number of waves with different amplitude and frequency to coexist in the same region of space. In fact, we are constantly bathed in a jumble of electromagnetic waves at all possible frequencies – especially if you are in a room full of people who are all using their cell phones.

As Heinrich Hertz had already realized in his original experiments, a good way of picking out the electromagnetic waves you would like to detect is by using the phenomenon of resonance. Radios are "tuned" to respond to just one of the many frequencies of electromagnetic waves that surround us, by adjusting the resonance frequency of an LRC circuit (or a comparable device). The circuit then produces large currents only in response to radio waves with frequencies near resonance, and the average value of the current follows the amplitude of those specific waves.

Watch this lecture, which accompanies our textbook.