Lesson Notes By Weeks and Term v4 - SHS 3

ALTERNATING CURRENT

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Subject: Physics

Class: SHS 3

Term: 2nd Term

Week: 6

Grade code: 3.3.2.LI.3

Strand code: 3

Sub-strand code: 2

Content standard code: 3.3.2.CS.1

Indicator code: 3.3.2.LI.3

Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS

Subtheme: ALTERNATING CURRENT

Lesson Video

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Performance objectives

Define alternating current (AC) and alternating voltage (AV).
Explain peak current (Io), peak voltage (Vo), and root mean square (RMS) values.
Calculate RMS values from peak values.
Illustrate the behavior of alternating current using graphs.
Discuss the importance of AC in Ghana's energy sector.

Lesson summary

Welcome, future engineers and scientists! Today, we are exploring a topic that powers our daily lives in Ghana: Alternating Current (AC). Every time you plug in your phone charger, turn on the fan, watch television, or use a refrigerator, you are using AC electricity supplied by the Electricity Company of Ghana (ECG). Unlike the Direct Current (DC) you get from batteries, AC has unique properties that make it perfect for powering our homes and industries. This lesson will demystify AC by looking at the mathematics that describes it. We will learn how to talk about its strength not just by its maximum value, but by its effective value, which is what appliance ratings are based on.

Lesson notes

Part 1: Defining Alternating Current (AC) and Voltage (AV)

Unlike Direct Current (DC) from a battery, which flows in only one direction, Alternating Current (AC) is a current that periodically reverses its direction. It flows back and forth.

Imagine pushing a swing. You push it forward, it comes back, you push it again. AC is like that. This back-and-forth motion can be perfectly described by a sine or cosine wave.

Visual Representation: DC Current: A straight, flat line on a current-time graph. AC Current: A sinusoidal wave (sine wave) on a current-time graph, oscillating between a maximum positive value and a maximum negative value.

Evaluation guide

Using mathematical relationships define Alternating current and alternating voltage.
Collaborative learning : Using the videos and simulation as well as internet/reference books let
learners research to find the meaning of the following (i) Peak current Io, (ii) Peak voltage Vo, (iii)
Root mean square value of alternating current Irms (iv) root mean square value of alternating