Lesson Notes By Weeks and Term v4 - SHS 3
ALTERNATING CURRENT
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ALTERNATING CURRENT
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Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 5
Grade code: 3.3.1.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 3.3.2.CS.1
Indicator code: 3.3.1.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ALTERNATING CURRENT
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Welcome, students. Today, we are exploring a concept that powers our daily lives: Alternating Current, or AC. Every time you plug in a fan, charge your phone, or watch television, you are using AC supplied by the Electricity Company of Ghana (ECG). Unlike the Direct Current (DC) from a battery that flows in one direction, AC constantly changes its direction and strength. Understanding AC is crucial for understanding how electricity is generated at places like the Akosombo Dam, transmitted across the country, and used safely in our homes. In this lesson, we will learn to describe AC, understand its key properties, and perform calculations that relate to the electricity we use every day.
Part 1: What is Alternating Current (AC)?
Alternating Current (AC) is a type of electric current in which the flow of electric charge periodically reverses direction. This is in contrast to Direct Current (DC), where the electric charge flows in only one direction. AC: Think of someone pushing a swing. They push forward, then pull back, repeating this cycle. The swing (charge) moves back and forth. DC: Think of pushing a box across the floor. You push continuously in one direction. The box (charge) moves in a straight line.
Graphical Representation: DC Voltage/Current: A straight horizontal line on a graph of Voltage vs. Time. AC Voltage/Current: A wave that goes above and below the time axis, indicating the change in direction and magnitude. Part 2: Types of AC Waveforms
While there are many types of AC waveforms, we will focus on three common ones. Sinusoidal Wave: Description: This is the most common and fundamental type of AC. It has a smooth, repetitive, wave-like shape. The voltage or current varies as the sine of time. Source: Generated by rotating generators, like those used by the VRA/ECG. This is the type of AC that powers our homes. Sketch: Square Wave: Description: This wave abruptly switches between two fixed voltage levels (one positive, one negative). It spends no time transitioning between them. Source: Commonly found in digital electronics, computers, and timers. Sketch: Triangular Wave (or Sawtooth Wave): Description: This wave has a constant, linear ramp up and then a constant, linear ramp down. A sawtooth wave is a special case where the ramp down is almost instantaneous. Source: Used in sound synthesizers and for generating signals in electronic test equipment. Sketch: