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: 12
Grade code: 2.3.2.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 2.3.2.CS.2
Indicator code: 2.3.2.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROMAGNETISM
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This lesson explores the fundamental principle that makes electric motors work: the turning effect, or torque, experienced by a coil carrying an electric current when it is placed in a magnetic field. This principle is at the heart of countless devices we use every day in Ghana. From the fan that cools us in the classroom, to the blender in the kitchen for making groundnut soup, to the starter motor in a 'trotro', understanding this concept is key to understanding our modern world. We will break down why this turning effect happens and learn how to calculate its strength.
2.1. The Foundation: The Motor Effect Before we talk about a whole coil, let's remember the basic principle, often called the motor effect:
> When a wire carrying an electric current is placed in a magnetic field, it experiences a force.
The magnitude of this force (F) is given by the formula: F = BILsinθ Where: F is the force on the wire (in Newtons, N) B is the magnetic field strength (in Tesla, T) I is the current in the wire (in Amperes, A) L is the length of the wire inside the magnetic field (in metres, m) θ is the angle between the wire and the direction of the magnetic field. 2.2. Finding the Direction: Fleming's Left-Hand Rule How do we know which way the wire will move? We use Fleming's Left-Hand Rule.
Imagine your left hand held out as shown below: Your Thumb points in the direction of the Thrust or Force (Motion). Your Forefinger points in the direction of the magnetic Field (from North to South pole). Your Centre finger points in the direction of the Current (conventional current, from + to -).