Mutual-inductance and transformers

Magnetic fields cause electrons in unconnected conductors to influence each other. This effect is called mutual inductance.

To make the effect strong, coils of wire are wound together on a core (which again has the effect of concentrating the magnetic field). This is called a transformer.

The coil of a transformer into which you put current is called the ‘primary’.

The coil(s) from which you take current are the ‘secondary(s)’.

The ‘turns ratio’ of a transformer is the ratio of the number of turns on the primary to those on the secondary. And conveniently are formulated FORMULA where Tp and Ts are the number of turns on primary and secondary, respectively, and Vp and Vs the voltages.

When we apply AC voltage to the primary, we get AC from the secondary. And, econdary, respectively, and Vp and Vs the voltages.

Transformers are very useful in certain situations, the most common being the passing of a signal from one part of a circuit to another while keeping the two electrically isolated.

Virtually all equipment connected to the AC mains supply is done so via a transformer.

For safety reasons this is a special type, designed to have good electrical isolation. We never use anything but a proper mains transformer for this!

Transformers are also very useful in many other circuits, and many other special types exist

Excerpt from: “Electronics Calculations Data Handbook” by Daniel McBrearty. Scribd.

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