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.2
Strand code: 3
Sub-strand code: 3
Content standard code: 3.3.3.CS.1
Indicator code: 3.3.3.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROMAGNETIC INDUCTION & APPLICATIONS
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Welcome, students! Today, we delve into one of the most foundational principles of modern technology: Electromagnetic Induction. This isn't just an abstract concept; it's the reason we can power our homes, charge our phones, and run our industries. Think about the Akosombo Dam generating electricity for the nation, or the small generator ("gen set") that keeps the lights on during a power outage ("dumsor"). At the heart of these machines is the principle we will study today, discovered by scientists like Michael Faraday. By understanding how a changing magnetic field can create electricity, you will understand the very core of our electrical world.
2.1. Magnetic Flux (Φ) Before we can understand induction, we must first understand magnetic flux. Definition: Magnetic flux is a measure of the total number of magnetic field lines passing through a given area. It quantifies the "amount" of magnetic field going through a surface. Analogy: Imagine rain falling straight down. If you hold a bucket with a large opening flat, you catch a lot of rain. This is high flux. If you tilt the bucket, the effective opening facing the rain becomes smaller, and you catch less rain. This is lower flux. If you hold the bucket sideways, no rain enters. This is zero flux. Formula: The magnetic flux (Φ) through a flat area (A) in a uniform magnetic field (B) is given by: Φ = B A cos(θ) Where: Φ is the magnetic flux, measured in Webers (Wb). B is the magnetic field strength, measured in Tesla (T). A is the area of the surface, measured in square meters (m²). θ is the angle between the magnetic field lines and the normal (a line perpendicular) to the surface area. When the field is perpendicular to the surface (θ = 0°), cos(0°) = 1, and flux is maximum: Φ = BA. When the field is parallel to the surface (θ = 90°), cos(90°) = 0, and flux is zero: Φ = 0. 2.2. Faraday's Discovery and Experiments Michael Faraday, a brilliant experimental physicist, reasoned that if an electric current could produce a magnetic field (as Oersted discovered), then perhaps a magnetic field could produce an electric current. He performed several key experiments.
Experiment 1: Moving Magnet and a Coil Setup: A coil of wire is connected to a galvanometer (a sensitive ammeter that shows both magnitude and direction of current). A bar magnet is held nearby. Observations: When the magnet is stationary, the galvanometer reads zero. A static magnetic field does not induce a current. When the North pole of the magnet is pushed into the coil, the galvanometer deflects, showing a current is induced. When the magnet is held stationary inside the coil, the deflection returns to zero. When the North pole is pulled out of the coil, the galvanometer deflects in the opposite direction. Moving the magnet faster produces a larger deflection (a larger induced current). Using a stronger magnet or a coil with more turns also produces a larger current.
Conclusion: A current is induced in a coil only when the magnetic flux through the coil is changing. The magnitude of the induced current depends on the rate at which the flux changes. 2.3. Faraday's Law of Electromagnetic Induction From his experiments, Faraday formulated his law: Statement: The magnitude of the induced electromotive force (e.m.f.) in a circuit is directly proportional to the rate of change of magnetic flux linkage through the circuit. Electromotive Force (e.m.f., ε): This is the "voltage" created by induction. It's the work done per unit charge, and it's what drives the induced current. It is measured in Volts (V). Magnetic Flux Linkage: This is the product of the number of turns in the coil (N) and the magnetic flux (Φ) through each turn. (Flux Linkage = NΦ). Formula: ε = -N (ΔΦ / Δt) Where: ε is the induced e.m.f. (in Volts, V). N is the number of turns in the coil. ΔΦ is the change in magnetic flux (Φ_final - Φ_initial), in Webers (Wb). Δt is the time taken for the change, in seconds (s). ΔΦ / Δt is the rate of change of magnetic flux. The negative sign (-) is crucial and is explained by Lenz's Law.