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: 8
Grade code: 3.3.2.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 3.3.2.CS.2
Indicator code: 3.3.2.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ALTERNATING CURRENT
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Welcome, learners! We are all familiar with the electricity provided by the Electricity Company of Ghana (ECG) that powers our homes, schools, and communities. This electricity is not like the direct current (DC) from a battery. It is Alternating Current (AC), which constantly changes direction. This unique nature of AC means that its interaction with circuit components like capacitors and inductors is different and more complex than in DC circuits. Today, we will explore the different types of opposition that AC encounters as it flows through a circuit. Just as a car faces resistance from the air and the road, AC faces opposition from resistors, capacitors, and inductors.
Part 1: Revisiting Resistance in AC Circuits
You already know about resistance (R) from your study of DC circuits. Resistance is the opposition to the flow of current, which causes a conversion of electrical energy into heat (Joule heating). Key Idea: A pure resistor behaves the same way in an AC circuit as it does in a DC circuit. Its opposition does not depend on the frequency of the alternating current. The voltage across a resistor (Vᵣ) is always in phase with the current (I) flowing through it. This means they reach their maximum and zero values at the same time. Unit: Ohm (Ω). Part 2: Introducing Reactance (X)
Reactance (X) is the opposition to the flow of alternating current offered by inductors and capacitors. Unlike resistance, reactance does not dissipate energy as heat. Instead, it relates to the energy temporarily stored in the electric or magnetic fields of the components. A crucial feature of reactance is that it depends on the frequency (f) of the AC supply.
There are two types of reactance: A. Inductive Reactance (Xₗ)