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: 7
Grade code: 3.3.2.LI.3
Strand code: 3
Sub-strand code: 2
Content standard code: 3.3.2.CS.2
Indicator code: 3.3.2.LI.3
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ALTERNATING CURRENT
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In our homes and businesses across Ghana, we use electricity supplied by the Electricity Company of Ghana (ECG) or NEDCo. This electricity is almost always Alternating Current (AC). We pay for this electricity based on our consumption, but have you ever considered that not all the electrical energy supplied to our appliances does useful work? Devices with motors, like fans, refrigerators, and air conditioners, consume a type of power that doesn't contribute to the main task (e.g., cooling or spinning) but is necessary for the device to function. This lesson explores the different types of power in AC circuits.
A. Review: Power in DC Circuits vs. AC Circuits
In a simple DC circuit with only resistors, the voltage and current are in phase. Power is straightforward: Power (P) = Voltage (V) × Current (I). The unit is Watts (W).
In AC circuits containing inductors (e.g., coils in motors, fans) and/or capacitors, the current and voltage are no longer in phase. Inductors cause the current to lag behind the voltage. Capacitors cause the current to lead the voltage.
This phase difference, represented by the angle phi (φ), is the key to understanding power in AC circuits. It means that the simple formula P = IV is no longer the full story. B. The Three Types of Power in AC Circuits