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: 11
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 concept of electromagnetic switches, most commonly known as relays. We have already learned that an electric current can create a magnetic field. Today, we will explore one of the most powerful and useful applications of this principle. Electromagnetic switches are hidden heroes in our daily lives, found in cars, refrigerators, traffic lights, and automatic water pump systems. Understanding how they work is key to appreciating the link between electricity, magnetism, and modern technology.
A. Recap: The Electromagnet Before we discuss the switch, let's remember what an electromagnet is. An electromagnet is a temporary magnet created when an electric current flows through a coil of wire wrapped around a soft iron core. Key Principle: When the current is ON, the iron core becomes a strong magnet. When the current is OFF, the iron core loses its magnetism. This ability to turn magnetism on and off with electricity is the foundation of the electromagnetic switch. B. What is an Electromagnetic Switch (Relay)? An electromagnetic switch, more commonly called a relay, is a device that uses a small electric current in one circuit to switch a much larger electric current ON or OFF in a separate circuit.
Think of it like this: You use your small finger to press a button that causes a large, heavy gate to open. Your finger doesn't push the gate directly. It activates a motor that does the heavy work. A relay does the same thing for electricity.
The main purposes of a relay are: Safety: It allows a person to use a low-voltage, low-current switch (which is safe to touch) to control a high-voltage, high-current circuit (which could be dangerous). Automation: It allows a small electronic signal from a sensor (like a light sensor or temperature sensor) to control a high-power device (like a street lamp or an air conditioner). Convenience: It allows a device to be controlled from a distance without running thick, expensive high-power cables all the way to the switch. C. Construction of a Simple Relay A simple relay has two main circuits and several key parts. Circuit 1: The Control Circuit (Input Circuit): This is the low-power circuit. It contains the electromagnet and the switch that activates it. Circuit 2: The Load Circuit (Output Circuit): This is the high-power circuit. It contains the high-power source, the device being controlled (e.g., a motor, a lamp), and the contacts of the relay.
Key Components: Electromagnet: A coil of insulated wire wrapped around a soft iron core. Armature: A movable piece of iron pivoted above the electromagnet. Spring: A small spring that holds the armature away from the electromagnet when there is no current. Contacts: Two points that act as the switch for the high-power circuit. One is fixed, and the other is attached to the moving armature.