Lesson Notes By Weeks and Term v4 - SHS 2
ELECTROMAGNETISM
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
ELECTROMAGNETISM
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 2
Term: 2nd Term
Week: 6
Grade code: 2.3.2.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 2.3.2.CS.1
Indicator code: 2.3.2.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROMAGNETISM
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
My dear students, we have all seen electric motors at work. They are in the fan that cools you in the classroom, the blender your mother uses to grind pepper, and the water pump that fills the "Polytank" at home. Have you ever wondered how electricity makes these things spin? The secret lies in a fascinating principle called electromagnetism. Today, we will explore the very heart of how these devices work. We will learn that when you pass an electric current through a wire placed in a magnetic field (like near a magnet), the wire experiences a force—a push or a pull. This is called the motor effect.
(30 mins) A. The Fundamental Idea: The Motor Effect
When a wire carrying an electric current is placed within a magnetic field, it experiences a force. This is because an electric current is essentially a flow of moving charges (electrons). We already know that a magnetic field exerts a force on a *single* moving charge. Therefore, it will exert a collective force on the millions of moving charges that make up the current in the wire.
This phenomenon is called the Motor Effect because it is the principle that makes electric motors rotate. B. Factors Affecting the Magnitude of the Force
Let us discuss the factors that make this force stronger or weaker. Imagine we have a wire placed between the North and South poles of two magnets. Magnetic Field Strength (B): Explanation: This refers to how strong the magnet is. A more powerful magnet creates a denser, stronger magnetic field. If you place the wire in a stronger magnetic field, it will experience a greater force. Think of it like swimming against a current; a stronger water current pushes you harder. Relationship: The force (F) is directly proportional to the magnetic field strength (B). `F ∝ B` Unit: The S.I. unit for magnetic field strength is the Tesla (T). Electric Current (I): Explanation: The current is the rate of flow of charge. A larger current means more charges are flowing through the wire every second. Since the magnetic field acts on each moving charge, a greater number of charges will result in a larger total force. Relationship: The force (F) is directly proportional to the current (I). `F ∝ I` Unit: The S.I. unit for current is the Ampere (A). Length of the Conductor (l): Explanation: This refers specifically to the length of the wire that is *inside* the magnetic field. If a longer section of the wire is exposed to the magnetic field, more moving charges within that section will be acted upon, resulting in a greater overall force. Relationship: The force (F) is directly proportional to the length (l) of the conductor within the field. `F ∝ l` Unit: The S.I. unit for length is the metre (m). Angle (θ) between the Conductor and the Magnetic Field: Explanation: The orientation of the wire matters! The force is at its maximum when the wire is perpendicular (at 90°) to the magnetic field lines. As the wire becomes more parallel to the field lines, the force weakens. If the wire is perfectly parallel (at 0° or 180°) to the magnetic field, there is zero force. The effective interaction is captured by the sine of the angle. Relationship: The force (F) is proportional to the sine of the angle (θ) between the wire and the magnetic field. `F ∝ sinθ` C. The Mathematical Formula