Lesson Notes By Weeks and Term v4 - SHS 3
ELECTROMAGNETIC INDUCTION & APPLICATIONS
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ELECTROMAGNETIC INDUCTION & APPLICATIONS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 10
Grade code: 3.3.3.LI.3
Strand code: 3
Sub-strand code: 3
Content standard code: 3.3.3.CS.2
Indicator code: 3.3.3.LI.3
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROMAGNETIC INDUCTION & APPLICATIONS
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Welcome, future scientists and engineers! Today, we are exploring a fascinating concept: how electrical components can store energy. We all know about batteries storing chemical energy. But did you know that a simple coil of wire, called an inductor, can store energy in a magnetic field? This principle is vital for many devices we use daily here in Ghana, from the fluorescent lights in our classrooms and the chargers for our phones to the power supply systems managed by the ECG. Understanding this helps us see the invisible forces at work in the technology that powers our lives.
A. Recap: What is an Inductor? An inductor is simply a coil of wire, often wound around a core material (like iron or even air). Its primary property is inductance (L), measured in Henrys (H).
B. Self-Inductance: Electrical Inertia Recall Faraday's Law: A changing magnetic flux through a coil induces an electromotive force (EMF) or voltage. Recall Lenz's Law: This induced EMF always opposes the change that caused it.
Now, let's apply this to a single inductor. When you pass a current (I) through the coil, it creates a magnetic field around it. If you try to *increase* the current, the magnetic field gets stronger. This *change* in the magnetic field induces a "back EMF" in the coil itself. According to Lenz's Law, this back EMF will oppose the increase. It tries to push current in the opposite direction, making it harder to increase the main current. Similarly, if you try to *decrease* the current, the magnetic field weakens. This change also induces an EMF, but this time it tries to *boost* the current to keep it from falling.
The Analogy with Kinetic Energy (Talk for Learning): This opposition to change is very similar to inertia in mechanics. Mechanical Inertia: An object with mass (m) resists a change in its velocity (v). To get a stationary fufu pestle moving, you must apply a force to overcome its inertia. Once it's moving, it has kinetic energy (KE = ½mv²). Electrical Inertia: An inductor with inductance (L) resists a change in the current (I) flowing through it. To get current flowing or to change it, a voltage source must do work against the back EMF. Once the current is flowing, the inductor has stored energy in its magnetic field.