# The limitations of a simple model for

1. Mar 13, 2005

### LoBun

...radio transmission.. what could they be?

Not exactly Maths, I know, but its Maths that I need it for..

Thanks!

Last edited: Mar 13, 2005
2. Mar 13, 2005

### HallsofIvy

I'm not sure what you would consider a model but I've seen this in differential equations texts:

Suppose we have an electrical circuit consisting of variable resistance, capacitor, and coil. The charge on the capacitor (whose derivative is the currant in the circuit) is given by
$$L\frac{d^2Y}{dt^2}+ \frac{1}{C}\frac{dY}{dx}+ Ry= 0$$
where L is the inductance, C the capacitance, and R the resistance in the circuit.
One can show that the solution is an alternating current that produces an electromagnetic wave.

If you have another circuit set up across the room, the waves from the first circuit will act as an external force on the second circuit. If the two circuits are identical (which can be done by altering the variable inductance, etc.) you have resonance so the very very tiny force of the waves will produce a noticable current in the second circuit.

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