Question:

What does this demonstration got to do with your handphone?

Answer:

This is a demonstration of the phenomenon called resonance: the amplitude of a forced oscillation is largest when the driving frequency matches the resonant frequency.

In this video, the “transmitter” tuning fork is struck so that it emits a sound wave of a specific freqeuncy. If the frequency of the sound wave matches closely the resonant frequency of the “receiver” tuning fork, resonance occurs. This allows for energy to be transferred from the “transmitter” to the “receiver” efficiently.

Cell phone communications work under the same principle. The telco’s antenna and your handphone’s antenna contain electronic circuits that oscillate at the same frequency. In other words, they are designed to transmit and receive electromagnetic waves of the same exact frequency (in the GHz region). If the frequencies are not matched, communication will not take place. This is also how different telcos can operate together: each telco is assigned a different frequency so that they do not interfere with one another.

Below is my own humble version of the same demonstration. It is less dramatic but I am parking it here just for sentimental reason.

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