Question

How could you use the idea of mutual inductance to transmit a signal, for example an audio signal, across a room?

Answer 1

Before answering your question, let's understand what is mutual inductance

In very very simple words, it is just the mutual understanding between two coils (wires) to transfer data. This data can be anything like voltage, current or any other signal like radio, audio.

In science and physics perspective, mutual inductance is the interaction of one coils magnetic field on another coil as it induces a voltage in the adjacent coil. When the emf is induced into an adjacent coil situated within the same magnetic field, the emf is said to be induced through Mutual induction. It means when two or more coils are magnetically linked together by a common magnetic flux, they have Mutual Inductance.

I hope the concept is now clear.

Now,

Let's see how we can transfer an audio signal. Suppose we have two coils in same magnetic field and having induced flux due to each other. Connect one coil to the radio and other coil to the speaker. We will notice that if we move the coils close to each other, the radio signal is transferred to speaker , the more closer we move the coil, more stronger the signal will be.

If we want to place these coils at greater distance but still want to get a good audio signal then we can increase the number of turns.

Here is the demonstration.