Lesson Notes By Weeks and Term v4 - SHS 3
ELECTROMAGNETIC INDUCTION & APPLICATIONS
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ELECTROMAGNETIC INDUCTION & APPLICATIONS
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Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 11
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, learners. Today, we are exploring a fascinating concept that powers many of the devices we use daily, from the charger for your phone to the ceiling fan in your room and the power grids that light up our communities. We will learn about inductors and how they act like "electrical energy reservoirs," storing energy not as charge, but in an invisible magnetic field. Understanding this principle is crucial for anyone interested in electronics, electrical engineering, or simply understanding how modern technology works. Think about pushing a heavy cart ("borla" truck). It's hard to get it moving because of its inertia. Once it's moving, it's also hard to stop suddenly.
a. What is an Inductor? An inductor is a passive electronic component that stores energy in a magnetic field when electric current flows through it. In its simplest form, an inductor is a coil of wire, sometimes wrapped around a magnetic core (like iron). Symbol:
 Key Property: Inductance (L). b. Inductance (L) Inductance is the property of an electrical conductor by which a change in current flowing through it induces an electromotive force (EMF) in both the conductor itself (self-inductance) and in any nearby conductors (mutual inductance). Think of inductance as electrical inertia. It is the measure of an inductor's opposition to a *change* in current. Unit: The SI unit of inductance is the Henry (H). Definition of the Henry: An inductor has an inductance of one Henry (1 H) if a current changing at a rate of one ampere per second (1 A/s) results in an induced EMF of one volt (1 V). `ε = -L (ΔI / Δt)` c. How is Energy Stored? The Step-by-Step Process
This is the core of our lesson. The storage of energy is not instant. It's a process of doing work against an opposing force. Current Starts to Flow: When a switch is closed in a circuit containing an inductor and a power source (like a battery), current begins to flow through the coil. Magnetic Field Builds Up: According to Oersted's discovery, any current creates a magnetic field. As the current increases from zero, the magnetic field around the coil grows stronger. This means the magnetic flux (Φ) through the coil is *changing*. Faraday's & Lenz's Laws Kick In: Faraday's Law of Induction states that a changing magnetic flux induces an EMF. Lenz's Law specifies the direction of this induced EMF. It will always act to *oppose the change that caused it*. The "Back EMF": In this case, the change is the *increase* in current. So, the inductor generates a "back EMF" that pushes against the flow of current from the battery. It tries to keep the current at zero. Work Must Be Done: The battery must do work to push the current against this back EMF. It's like pushing a piston into a cylinder of gas—you have to work against the pressure. Energy Storage: This work done by the battery is not lost (assuming a perfect inductor with no resistance). It is converted into potential energy and stored in the magnetic field that has been established in and around the inductor.
When the current reaches a steady, maximum value (I), the magnetic field is no longer changing. The back EMF disappears, and no more energy is stored. The stored energy remains in the field as long as the steady current is maintained.