Overview
This lesson introduces electrical circuits, their components, and how electricity flows, emphasizing the difference between electron flow and conventional current, as well as the role of resistors.
What is Electricity and a Circuit?
- Electricity is a form of energy used in homes, schools, and devices, called current electricity.
- Current electricity is the flow of electric charge (electrons) through a conductor.
- A circuit is a complete path that allows electric charges to flow.
- An electric charge can jump across a gap, causing a spark or a shock.
Main Parts of a Basic Circuit
- Conducting wires (usually metal) carry the electric current.
- A cell or battery stores chemical energy and converts it to electrical energy.
- Output devices (bulb, buzzer) change electrical energy into another form (light, sound, or heat).
- A switch controls if electricity can flow; closed (on) means current flows, open (off) means it does not.
Flow of Electricity: Electron vs Conventional Current
- Electrons move from the negative terminal to the positive terminal in a closed circuit.
- Conventional current (used in diagrams) flows from positive to negative, based on historical assumptions.
- Both models help understand how circuits work, though electron flow is the physical reality.
Energy Transfer in Circuits
- Energy converts from chemical (battery) to electrical (current) to light or heat (bulb).
- All appliances work by completing a circuit and transferring energy.
Role of Resistors in Circuits
- A resistor is a component that reduces or limits the current flow.
- Devices may be damaged without resistors controlling the current, especially during load shedding.
- When a resistor is added, the bulb shines dimmer because less current and energy reach it.
Measuring Circuit Properties
- Current is measured in amps (A).
- Voltage is measured in volts (V), representing potential power.
- Resistance is measured in ohms (Ω).
- Power used in circuits is measured in watts (W).
Circuit Symbols and Diagrams
- Straight lines represent wires.
- A zigzag line is a resistor.
- A circle with a cross is a bulb.
- A short and long line pair is a cell; multiple pairs form a battery.
- A gap is an open switch; a line connecting is a closed switch.
- A half-circle on two legs is a buzzer.
- Circuit diagrams use these symbols for clear scientific drawings of circuits.
Key Terms & Definitions
- Electricity — form of energy from the movement of electric charge.
- Current electricity — flow of electrons through a conductor.
- Circuit — complete path for electric current.
- Electron flow — movement of electrons from negative to positive terminal.
- Conventional current — flow from positive to negative terminal (diagram standard).
- Resistor — component that limits or reduces current flow.
- Voltage (V) — the potential power of a circuit.
- Current (A) — the rate of flow of charge.
- Resistance (Ω) — how much a component opposes current.
- Power (W) — energy used per second in a circuit.
Action Items / Next Steps
- Practice drawing a circuit diagram using the standard symbols.
- Complete the self-marking quiz linked in the lesson.
- Prepare for the next lesson on electrical currents.