Lesson Notes By Weeks and Term v4 - SHS 2
ELECTROMAGNETISM
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ELECTROMAGNETISM
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Subject: Physics
Class: SHS 2
Term: 2nd Term
Week: 8
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
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Good morning, class. Today, we are exploring a fascinating principle that powers many of the devices we use every day, from the fan that cools us down to the blender in the kitchen used for preparing fufu or soup, and even the starter motor in a car or "trotro". This principle, known as the motor effect, describes what happens when electricity meets magnetism. We will learn how a simple wire carrying current can be made to move by a magnetic field.
A. The Motor Effect: The Core Idea
When a wire carrying an electric current is placed in a magnetic field, it experiences a force. This phenomenon is called the motor effect.
Why does this happen? An electric current is simply a flow of moving charges (electrons). We already know that a magnetic field exerts a force on any single moving charge. Therefore, when you place a wire with billions of moving charges (the current) into a magnetic field, the field exerts a force on each charge, and the combined effect is a single, noticeable force on the wire itself. This force can cause the wire to move, jump, or bend. B. Factors Affecting the Magnitude of the Magnetic Force
The strength of the force (F) experienced by the wire is not constant. It depends on several factors. Let's discuss them one by one. Magnetic Field Strength (B) Explanation: This is how strong the magnet is. A more powerful magnet creates a stronger magnetic field. If you place the wire in a stronger magnetic field, it will experience a greater force. Think of it like trying to walk through a gentle breeze versus a strong harmattan wind; the stronger wind pushes you more. Relationship: The force (F) is directly proportional to the magnetic field strength (B). `F ∝ B` Unit: Magnetic field strength (also called magnetic flux density) is measured in Tesla (T). Electric Current (I) Explanation: The current is the rate of flow of charge. A larger current means more electrons are flowing through the wire per second. With more moving charges in the field, the total force exerted by the magnet will be greater. Relationship: The force (F) is directly proportional to the current (I). `F ∝ I` Unit: Current is measured in Amperes (A). Length of the Conductor (l) Explanation: This refers to the length of the wire that is *actually inside* the magnetic field. A longer piece of wire inside the field contains more moving electrons for the field to act upon, resulting in a larger overall force. Relationship: The force (F) is directly proportional to the length of the conductor in the field (l). `F ∝ l` Unit: Length is measured in metres (m). Angle between the Conductor and the Magnetic Field (θ) Explanation: The orientation of the wire relative to the magnetic field lines is very important. Maximum Force (θ = 90°): The force is strongest when the wire is perpendicular (at a right angle) to the direction of the magnetic field. Here, `sin 90° = 1`. Zero Force (θ = 0° or 180°): If the wire is placed parallel to the magnetic field lines, it experiences no force at all. The charges are moving along the field lines, not cutting across them. Here, `sin 0° = 0`. Intermediate Force: For any other angle between 0° and 90°, the force will be somewhere between zero and the maximum value. The `sin θ` term in the formula accounts for this. Relationship: The force (F) is proportional to the sine of the angle (sin θ). `F ∝ sin θ` C. The Mathematical Formula