Electromagnetic Induction (Basics)

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Electromagnetic Induction (Basics)

Author: oLahav

The basic concepts of electromagnetics

The basic law of electromagnetism is Faraday's Law of Induction. Michael Faraday was a pioneer in the fields of electromagnetism and electrochemistry during the 1800s, and one of the laws he formulated simply by observation remains the basis for electromagnetic induction.

The idea is simple: "The induced electromotive force or emf in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit." Let's break it down:
Electromotive force, emf, refers to the energy gained per unit charge passing through an electrical device (such as a generator). It's measured in Volts, and a source of emf is used to power up electrical circuits (like a battery).

Magnetic flux refers to the quantity of magnetism, or the strength of a given magnetic field.

In equation format, the law looks like this: $\epsilon = - \frac{d\phi_B}{dt}$ .

In super basic terms- an electric current can create a magnetic field, and vice versa.

It's important to distinguish between 2 different effects this law describes:

1. Motional EMF, which is generated by a magnetic force on a moving wire.

2. Transformer EMF, which is generated by an electric force due to a changing magnetic field.

There are 3 important applications to Faraday's law:

Electrical generator:

This device is used to generate electric current. The idea is that when a magnet is moved relative to a conductor (or the other way around), emf will be generated. Therefore, if you connect this whole thing to an electrical circuit, a current will flow. This means the mechanical energy (of moving the magnet) is converted to electrical energy. This is an important way of making electricity.

Here's an illustration:

Faraday's disc rotates, sweeping the conducting disc circularly in the static magnetic field B due to a permanent magnet. The magnetic force (v × B) causes electrical current to flow (due to Faraday's Law of Induction) radially across the conducting disc to the conducting rim, and from there the circuit path completes through the brush. Thus, current is generated from mechanical motion.

Electrical motors:

The opposite of a generator. Say you pass a current in a conductor, then a magnetic field will result, which can be used to rotate or move a magnet. This converts electrical energy into mechanical energy, and it forms the basis for early days, real-life motors.

In the earlier picture, imagine the opposite happening- an electrical current creating the magnetic field, which rotates the disc.

Electrical transformers:

These are a bit more hard to understand. Transformers (not the robots in disguise) transfer electrical energy from one circuit to another indirectly, through this sort of induction. It's actually pretty simple- circuit A flows using a load or a generator or something. Then it has to exert a magnetic field on circuit B (like a motor). That magnetic field induces a current in circuit B (like a generator), which causes electricity to flow.

Here's an illustration:

The primary (red) circuit creates a magnetic field, which passes through both coils. In the second (blue) coil, this generates a current.

Electromagnetic induction forms the basis for generators, motors and transformers, and without these, we wouldn't have commercial electricity at all. So we better say "thanks, Faraday!" for his important law.

Thanks Faraday! Electromagnetism rules!