Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Describe how inductors behave in AC and DC circuits.
• Explain the operation of a bicycle dynamo.
• Illustrate the workings of a simple AC generator.
• Discuss how to modify an AC generator into a DC generator.

Lesson summary

Welcome, future engineers and scientists! Today, we are exploring one of the most important principles in all of physics: Electromagnetic Induction. This is the magic behind how we generate almost all the electricity we use. Think about the lights in this room, the power from the Akosombo Dam, or even the small generator your family uses during a power outage ("dumsor"). All of these work because of the principles we will learn today. We will discover how moving a wire near a magnet can create electricity, and we will see how this idea is used to build machines like generators and dynamos that power our world.

Lesson notes

2.1 The Principle of Electromagnetic Induction

At the heart of our topic are two fundamental laws:

a) Faraday's Law of Electromagnetic Induction: This law states that whenever the magnetic flux linking a circuit changes, an electromotive force (e.m.f.) is induced in the circuit. The magnitude of this induced e.m.f. is directly proportional to the rate of change of the magnetic flux. In simple terms: If you change the magnetic field around a coil of wire, you create a voltage (e.m.f.) in that wire. How to change the magnetic flux: Move a magnet towards or away from a stationary coil. Move a coil towards or away from a stationary magnet. Rotate a coil within a magnetic field. Change the strength of the magnetic field (e.g., by changing the current in an electromagnet).

b) Lenz's Law: This law gives the direction of the induced current. It states that the direction of the induced current is always such that it opposes the very change that produced it. In simple terms: Nature doesn't like change. If you push a North pole of a magnet into a coil, the coil will induce a current that creates its own North pole to push back against you. If you pull it out, the coil will create a South pole to try and pull it back. This opposition is why we must do work to generate electricity, conserving energy.

Evaluation guide

• Discuss the behaviour of the inductor in a.c and d.c circuits.
• Talk for learning:
• Discuss the operations of a bicycle dynamo.
• Discuss the op erations of a simple a.c. generator .