Lesson Notes By Weeks and Term v4 - SHS 3
DIRECT CURRENT
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DIRECT CURRENT
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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: 3.2.2.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 direct current electricity: Ohm's Law. Understanding this law is crucial for analysing how electrical devices work. In Ghana, from charging our phones and using a standing fan to understanding why using the wrong charger can damage a device, the principles of voltage, current, and resistance are at play every day. This lesson will move from theory to a hands-on experiment, allowing us to see Ohm's Law in action and understand why some materials follow this law while others do not.
Part 1: The Building Blocks - Voltage, Current, and Resistance
Before we state Ohm's law, let's refresh our memory on the three key quantities involved. Imagine water flowing through a pipe from an overhead Polytank. Current (I): This is the flow of electric charge (electrons) through a conductor. It's like the *amount* of water flowing through the pipe per second. We measure current in Amperes (A) using an Ammeter connected in series. Voltage (V): Also known as Potential Difference (p.d.), this is the "push" or "pressure" that makes the charges flow. It's like the height difference of the Polytank that creates water pressure. We measure voltage in Volts (V) using a Voltmeter connected in parallel across a component. Resistance (R): This is the opposition to the flow of current. It's like a narrow section or blockage in the pipe that makes it harder for water to flow. All components in a circuit, including the wires themselves, have some resistance. We measure resistance in Ohms (Ω). Part 2: Ohm's Law
In the early 1800s, a German physicist named Georg Simon Ohm discovered a simple but powerful relationship between these three quantities.
> Ohm's Law states that the current (I) flowing through a metallic conductor is directly proportional to the potential difference (V) across its ends, provided that the temperature and other physical conditions of the conductor remain constant.