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: 12
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 engineers and scientists! Today, we delve into a fascinating concept: how a simple coil of wire, called an inductor, can store energy. This isn't just theory; it's the principle behind many devices we use daily. When you use a voltage stabilizer to protect your TV during power fluctuations from ECG, or see the flicker of a fluorescent tube light in our classroom, you are witnessing the effects of energy storage in inductors. We will explore how an inductor resists changes in electric current, much like a heavy object resists being pushed, and in doing so, stores energy in a magnetic field.
2.1. 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, it is a coil of wire. Symbol: The circuit symbol for an inductor is a coil: `~~~~` Function: Its primary function is to oppose any change in the electric current flowing through it. It has no effect on a steady, direct current (DC), but it strongly affects alternating current (AC) or any changing DC. 2.2. Inductance (L)
Inductance (L) is the property of an electrical conductor by which a change in current flowing through it induces an electromotive force (E.M.F.) in the conductor itself (self-inductance) and in any nearby conductors (mutual inductance). Think of inductance as "electrical inertia". Just as mass (inertia) in mechanics resists a change in velocity, inductance resists a change in current. S.I. Unit: The 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) induces a back E.M.F. of one volt (1 V) across it. Mathematically, the induced back E.M.F (ε) is given by: `ε = -L (dI/dt)` Where: `ε` is the back E.M.F. in Volts (V) `L` is the inductance in Henries (H) `dI/dt` is the rate of change of current in Amperes per second (A/s) The negative sign is due to Lenz's Law, indicating that the induced E.M.F. opposes the change in current. 2.3. The Process of Storing Energy in an Inductor
This is the core of our lesson. Let's break it down step-by-step. Initial State: Consider a simple circuit with a battery, a switch, and an inductor. Before the switch is closed, there is no current and no magnetic field. Closing the Switch: The moment you close the switch, the battery tries to push current through the inductor. The current begins to increase from zero. Building a Magnetic Field: As the current flows and increases, it creates a magnetic field around the coil. Because the current is increasing, the magnetic field is also growing (i.e., the magnetic flux is changing). Self-Induction (Faraday's & Lenz's Laws): According to Faraday's Law of Induction, a changing magnetic flux induces an E.M.F. in the coil. According to Lenz's Law, this induced E.M.F. (called a back E.M.F.) must oppose the change that created it. In this case, it opposes the *increase* in current from the battery. Doing Work: The back E.M.F. acts like a temporary "opposing battery." For the main battery to continue pushing current through the inductor, it must do work against this back E.M.F. Energy Storage: Where does the energy from this work go? It is not lost as heat (like in a perfect resistor). Instead, this work is converted into potential energy and is stored in the magnetic field that has been established around the inductor. Steady State: Once the current reaches a steady, maximum value (limited by the circuit's resistance), `dI/dt` becomes zero. The magnetic field is now constant, so the back E.M.F. disappears (ε = 0). The inductor now acts like a simple connecting wire, and no more energy is stored. The energy remains stored in the constant magnetic field as long as the steady current flows.