Lesson Notes By Weeks and Term v4 - SHS 3
DIRECT CURRENT
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DIRECT CURRENT
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 2
Grade code: 3.3.1.LI.2
Strand code: 3
Sub-strand code: 1
Content standard code: 3.3.1.CS.2
Indicator code: 3.3.1.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: DIRECT CURRENT
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This lesson introduces one of the most fundamental principles in the study of electricity: Ohm's Law. We use electricity every single day in Ghana – from charging our mobile phones and watching TV to using a refrigerator or an electric cooker. Understanding Ohm's Law helps us understand how these devices work and how they are designed to be safe and efficient. It explains the relationship between the "push" (voltage from the ECG or a battery), the "flow" (current), and the "opposition" (resistance) in any electrical circuit.
A. What is Ohm's Law?
Imagine you are trying to push water through a pipe. The amount of water that flows depends on two things: how hard you push (the pressure) and how narrow or blocked the pipe is (the resistance). Electricity works in a very similar way. Potential Difference (Voltage, V): This is the "electrical push" or pressure that makes charges move. It is supplied by a source like a battery or the ECG mains. It is measured in Volts (V). Current (I): This is the rate of flow of electric charge. It is the "amount of electricity flowing" through the circuit. It is measured in Amperes (A). Resistance (R): This is the opposition to the flow of current. A material with high resistance makes it difficult for current to flow, while a material with low resistance allows current to flow easily. It is measured in Ohms (Ω).
Ohm's Law, named after the German physicist Georg Ohm, states that:
> The current flowing through a metallic conductor is directly proportional to the potential difference across its ends, provided that physical conditions, such as temperature, remain constant.