Induction

In the previous set of lessons, we concentrated on the behaviour of moving charges in magnetic fields.
However there is a flip-side.
If an electrical charge experience is a changing magnetic field, or more correctly flux, it will begin to 'move'. This concept is called electromagnetic induction.
In the series of lessons we will discuss the key terms you need to understand, Faraday's law and Lenz law, which underpin our understanding of induction, and include some applications of induction, including transformers and electromagnetic braking.

1. Flux and EMF Explained

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An important concept in electromagnetic induction is the idea of flux. Flux has numerous meanings within physics. In this concept in this context we will be examining it in terms of magnetic field lines.
This video also discusses how electromotive force, or EMF for short, is related to the idea of flux change.

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2. Faraday's Law demonstrated and explained

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If a wire experiences a changing flux it also experiences an EMF, as discussed in the previous video. More correctly EMF that is generated is directly proportional to the rate of change of flux this is called Faraday's law.
This video demonstrates this in action and explains the principles behind Faraday's Law.

Check out the interactive which allows you to consolidate your understanding of Faraday's Law

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Explore faraday's Law with this pHET animation

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3. Eddy Currents and Lenz Law

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If a conductor experiences a changing flux, and thus experiences and EMF, if the charges are free to flow, currents are induced. In solid materials such as pipes and sheets of metal, these currents become eddy currents. However these eddy currents will therefore also generate their own magnetic fields thereby interacting with the magnetic field that generated them. This leads to an important principle called lenz' Law.
See the following two videos that demonstrate lenses law in action and also provides an application called electromagnetic breaking.

Down a Pipe
Drop a magnet down a pipe and it does not fall as you expect. Physics involved

Electromagnetic Braking
Similar to the lesson above, but now looking at electromagnetic braking

Many motion graph analysis video examine simplistic examples where velocity is constant or acceleration is constant. In this video I analyse a well known toy which has more complex motion, and I apply the same skills taught to analyse its graph. This video helps students consolidate their understanding of motion graphs, as well as review concepts such as friction, energy and forces.

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4. Motors and Generators compared

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Induction and AC motors

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Since a current bearing wire has a magnetic field, placing the same wire in an external magnetic field will mean it will experience a force. This is known as the motor effect.
See Resources for using a current balance which examine the motor effect

Induction and AC motors

In this video I discuss AC motors, in particular, synchronous motors. I then lead on to the physics behind induction motors

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5. Understanding Back EMF

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In the previous set of lessons we discussed the principles in an electric motor, that is a coil of current bearing wire will experience a force in a magnetic field. If in a loop this results in a torque and the motor turns. However the loop of wire is now experiencing a changing flux which should result in induction. This leads to important consideration called back EMF
The motor effect and induction at the same time!

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6. Transformers Explained

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The Induction Coil

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Most of us have heard of transformers. More than likely the device you are reading this on is plugged into either a 240 V or 120 V power supply, but only requires a much lower voltage. Do you have a transformer that transforms the higher voltage into the lower voltage. But how does it work? In essence it's a simple application of conservation of energy and Faraday's law. This video not only discusses the key principles but also the mathematical models associated with transformers.
Check out the sample solution, and try some problems yourself.
Also watch the video on the induction coil, which is used in many classrooms and is simply a transformer.

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