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: 9
Grade code: 2.3.2.LI.4
Strand code: 3
Sub-strand code: 2
Content standard code: 2.3.2.CS.2
Indicator code: 2.3.2.LI.4
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROMAGNETISM
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This lesson introduces the fundamental principle of electromagnetism: the idea that electricity and magnetism are not separate forces but are deeply connected. We will explore the discovery that an electric current can produce a magnetic field and learn how to describe and control this effect. This concept is the foundation for countless technologies we use every day in Ghana, from the electric motors in our fans and blenders to the loudspeakers at church or in our cars, and even the large cranes used in industrial areas like Tema or Takoradi. Understanding this link is crucial for understanding how our modern world is powered.
2.1 The Discovery of Electromagnetism: Oersted's Experiment
For a long time, scientists thought electricity and magnetism were two completely unrelated phenomena. This changed in 1820 with a discovery by a Danish scientist named Hans Christian Oersted. The Experiment: Oersted was giving a lecture and had a simple circuit set up on his desk. Nearby, he also had a magnetic compass. By chance, when he switched on the current in the wire, he noticed that the needle of the compass deflected (moved) from its usual North-South alignment. When he switched the current off, the needle returned to its original position. The Conclusion: This simple observation was revolutionary. A compass needle is a small magnet, and it only moves if there is another magnetic field nearby to exert a force on it. Therefore, Oersted concluded that an electric current flowing through a conductor creates a magnetic field around it. This is the foundational principle of electromagnetism. *Key takeaway:* Moving electric charges (current) produce magnetism. 2.2 Magnetic Field around a Straight Current-Carrying Conductor
When current flows through a long, straight wire, it produces a magnetic field. The shape and direction of this field follow specific rules. Shape: The magnetic field lines are a series of concentric circles with the wire at their centre. Imagine the wire is the axle of a bicycle wheel, and the spokes are the radius. The magnetic field lines are like the rim of the wheel. Direction: The direction of the magnetic field (which way the circles "flow") depends on the direction of the current. We use the Right-Hand Grip Rule to determine this.
The Right-Hand Grip Rule (for a Straight Wire): Imagine you are holding the wire with your right hand. Point your thumb in the direction of the conventional current (from positive to negative). The direction in which your fingers curl around the wire represents the direction of the magnetic field lines.