# Overview of Electromagnetic Induction

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After completing this lesson, you will be able to explain what electromagnetic induction is and describe how it is used to generate electricity in our everyday lives. A short quiz follows the lesson.

## What is Electromagnetic Induction?

Electromagnetic induction is the production of an electric current created because of a varying magnetic field. The reason this works is complex, but whenever a magnetic field is changing and a conductor is present inside it, electricity is produced.

This is a wonderful thing, because it's how we generate electricity in all power plants. Something in the power plant pushes a turbine: that force can be steam created from burning coal, or the nuclear reactions in a nuclear power plant, or the wind pushing the turbine directly.

Whatever the cause, the turbine turns inside a magnetic field. And that produces electricity which we can use to power our homes.

This same principle is also used in transformers, which take electricity and change the voltage. For example, the voltages in our homes are fairly small: 110 volts in the USA, 230 volts in many European countries. But if we transferred electricity across the country at these voltages, we would lose a lot of energy to heat. So instead, we use a transformer to STEP UP the voltage to really high numbers for transport, and then another transformer acts to STEP DOWN the voltage to what we need in our homes. And this all works on the principle of electromagnetic induction.

Induction is used in lots of everyday applications, like induction motors, induction cookers, and induction welding. All these things are particularly notable for how energy efficient they are.

## How Can a Magnetic Field be Varied?

There are numerous ways to vary a magnetic field. Faraday's law tells us that the voltage generated is proportional to several things: the number of loops in the coil of wire you're generating electricity in, the magnetic field strength, and the cross-sectional area of the coil at 90 degrees to the magnetic field.

This might seem a bit complicated, but for practical purposes it means there are multiple ways you can vary a magnetic field to produce electricity. You can:

• Move the coil in and out of the edge of the magnetic field to change the cross-sectional area that's inside it.
• Rotate the coil, which also changes the cross-sectional area found inside the magnetic field.
• Change the strength of the magnetic field (if you're using an electromagnet that can be controlled)

Using any of these approaches will produce electricity. Rotating the coil is the most common one, and it is the method used in power plants.

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