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: 1
Grade code: 3.3.1.LI.1
Strand code: 3
Sub-strand code: 1
Content standard code: 3.2.2.CS.2
Indicator code: 3.3.1.LI.1
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: DIRECT CURRENT
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This lesson introduces the fundamental concepts of Direct Current (D.C.) electricity. While we get our power from the national grid (ECG) as Alternating Current (A.C.), many of the devices we use daily rely on D.C. power. Think about your mobile phone, the torchlight you use during a power outage ("dumsor"), your laptop, and the remote control for your TV. All these are powered by batteries, which are D.C. sources. Understanding D.C. circuits is the first step to understanding how all these essential gadgets work. This knowledge is crucial for anyone interested in engineering, electronics, or even basic home repairs.
This section breaks down the essential ideas you need to master. 2.1. Basic Circuit Components and States
An electric circuit is a closed path through which electric current can flow. The simplest circuit has three main parts: Source: The provider of electrical energy. In D.C. circuits, this is usually a cell or a battery (a collection of cells). The source provides the "push" or electromotive force (EMF) to move the charges. *Example: A 1.5V AA battery (like Star Battery or ABC).* Load: The component that uses the electrical energy and converts it into another form (light, heat, sound, etc.). It provides resistance in the circuit. *Example: A light bulb, a resistor, your phone's charging circuit.* Switch (or Key): A device that is used to open or close the circuit, controlling the flow of current.
The state of a circuit can be: Closed Circuit: An uninterrupted, complete path for current to flow from the source, through the load, and back to the source. The switch is "ON". Open Circuit: A broken or incomplete path. No current can flow because there is a gap (e.g., the switch is "OFF"). 2.2. Fundamental Electrical Quantities Electric Charge (Q): A fundamental property of matter. It can be positive or negative. The smallest unit of charge is the charge on a single electron or proton. Unit: Coulomb (C). The charge of one electron is -1.6 x 10⁻¹⁹ C. 1 Coulomb is the total charge of approximately 6.24 x 10¹⁸ electrons. Electric Current (I): The rate of flow of electric charge through a point in a circuit. Formula: `I = Q / t` (where Q is charge in Coulombs, t is time in seconds). Unit: Ampere (A), often called 'amps'. 1 Ampere means 1 Coulomb of charge is flowing past a point every second. 2.3. Conventional Current vs. Electron Flow
This is a very important historical distinction. Electron Flow: This is what *actually* happens inside the metal wires. The source (battery) creates an electric field that forces the free electrons (which are negatively charged) to move. They flow from the negative terminal, through the circuit, to the positive terminal. Conventional Current: Early scientists, before the discovery of the electron, assumed that current was the flow of *positive* charges. Therefore, they defined current as flowing from the positive terminal to the negative terminal.