Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define key terminologies of DC circuits.
• Explain the difference between conventional and electron flow.
• Calculate total resistance and current using Ohm's Law.
• Draw and label simple circuit diagrams.

Lesson summary

This lesson introduces the fundamental concepts of Direct Current (DC) electricity, the type of electricity that powers our mobile phones, laptops, torches (flashlights), and remote controls. While the power we get from the Electricity Company of Ghana (ECG) is Alternating Current (AC), almost every portable electronic device relies on DC from batteries. Understanding how DC circuits work is essential for understanding electronics and how these everyday devices function. We will explore the key components of a circuit, define the quantities that describe electricity, and learn how to calculate them.

Lesson notes

This section breaks down the core ideas you need to master. We will build our understanding step-by-step. 2.1. The Simple Electric Circuit

An electric circuit is a complete path through which electric charge can flow. For a circuit to work, it must have at least three basic components: Source: Provides the energy or "push" to make the charges move. In DC circuits, this is usually a battery or a cell. It converts chemical energy into electrical energy. Load: A device that uses the electrical energy and converts it into another form (light, heat, sound, motion). Examples: a light bulb, a resistor, a fan, your phone's processor. Connecting Wires: Made of conductive materials (like copper) that provide a path for the charge to flow from the source, through the load, and back to the source. Switch (or Key): A device that can open or close the circuit, controlling the flow of current. Closed Circuit: An unbroken, complete path. The switch is 'ON', and current flows. Open Circuit: A broken path. The switch is 'OFF', and no current can flow.

Analogy: Think of a water pumping system. The pump is the source (battery). The water is the electric charge. The flow of water is the electric current. A turbine that does work is the load (bulb). The pipes are the connecting wires. A valve is the switch. 2.2. Fundamental Electrical Quantities

| Quantity | Symbol | Unit | Definition & Explanation | | :--- | :--- | :--- | :--- | | Electric Charge | Q | Coulomb (C) | The fundamental property of matter that experiences a force when placed in an electromagnetic field. In circuits, the charge carriers are usually electrons. | | Electric Current | I | Ampere (A) | The rate of flow of electric charge. It tells us how much charge passes a point in the circuit per second. Formula: `I = Q / t` (where Q is charge in coulombs, t is time in seconds). 1 Ampere = 1 Coulomb per second. | | Resistance | R | Ohm (Ω) | The opposition to the flow of electric current. The load in a circuit provides resistance. Good conductors have low resistance; insulators have very high resistance. | | Potential Difference (p.d.) | V | Volt (V) | Also known as voltage. It is the work done (or energy converted) in moving a unit of positive charge from one point to another. It is the "energy used" by the load. Formula: `V = W / Q` (where W is work done in Joules). We measure p.d. *across* a component (e.g., across a bulb). | 2.3. Ohm's Law

Evaluation guide

• Demonstrate an
• understanding of
• current electricity and
• its related quantities.Explain the key terminologies of circuitry and how they are related to one another.