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: 10
Grade code: 2.3.2.LI.3
Strand code: 3
Sub-strand code: 2
Content standard code: 2.3.2.CS.2
Indicator code: 2.3.2.LI.3
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROMAGNETISM
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This lesson explores the fascinating application of magnetic forces on electric currents, a principle known as the motor effect. We will see how this simple principle is used to build two incredibly important devices: the electric motor, which powers everything from the fan in our classrooms to the blender in our kitchens, and the moving coil galvanometer, the ancestor of modern meters used to measure electricity. Understanding these devices is key to appreciating the technology that drives our modern world, from the local corn mill (`nikanika`) to large industrial machines.
2.1 The Foundational Principle: The Motor Effect
Before we can understand motors or galvanometers, we must understand the fundamental principle that makes them work. Definition: The motor effect is the phenomenon where a conductor carrying an electric current experiences a force when placed in a magnetic field. Reason: The electric current in the wire creates its own magnetic field. This field interacts with the external magnetic field (from a permanent magnet or electromagnet), resulting in a force. Direction of Force - Fleming's Left-Hand Rule: This rule helps us predict the direction of the force (or motion). Hold the thumb, forefinger, and middle finger of your left hand mutually perpendicular to each other (like an 'L' shape with the middle finger pointing out). Forefinger points in the direction of the Magnetic Field (North to South). Centre finger (middle finger) points in the direction of the Current. Thumb points in the direction of the Thrust or Force (Motion). Magnitude of the Force: The size of the force (F) depends on: The strength of the magnetic field (B) The size of the electric current (I) The length of the conductor in the field (L) The angle (θ) between the conductor and the magnetic field. The formula is: F = BIL sin(θ). The force is maximum when the conductor is perpendicular (θ = 90°) to the field. 2.2 The Direct Current (DC) Electric Motor
A motor is a device that converts electrical energy into mechanical energy (rotational motion).
Structure and Key Parts: A simple DC motor consists of the following essential parts.