Making Use of Electricity - Simple Circuits

Making Use of Electricity - Simple Circuits

• A closed circuit forms a complete loop, allowing electricity to flow. An open circuit does not.
• For an appliance to work, it needs a source of electrical energy (like a battery or cell) and a closed electrical circuit.
• Electrical conductors allow electricity to flow (e.g., metal, pencil lead, vinegar).
• Electrical insulators prevent electricity from flowing (e.g., plastic, wood, distilled water).
• A switch is used to open or close a circuit.

Circuit Symbols

• Circuit components have specific symbols. The symbols for a cell, battery, switch and connecting wire are shown in the diagrams.

Drawing Circuit Diagrams

• Circuit diagrams use symbols to represent components.
• Straight lines represent wires.
• Dots mark the connection points of wires.

Current

• Electric current is the flow of electric charges.
• Current flows from the positive terminal of a cell to the negative terminal.
• An ammeter measures current in amperes (A).
• When connecting an ammeter, the red lead connects to the positive terminal and the black lead to the negative terminal. Never connect an ammeter directly to a cell.

Voltage

• Voltage indicates the energy supplied to electric charge by a cell.
• A voltmeter measures voltage in volts (V).
• A voltmeter is connected across a cell to measure voltage. The red lead connects to the positive terminal and the black lead to the negative terminal.
• Adding cells in the same direction increases the voltage. Adding cells in opposite directions decreases the voltage.
• Higher voltage means more flow of current.

Resistance

• Resistance opposes the flow of current. The unit of resistance is the ohm (Ω).
• A resistor is a circuit component that has a specific resistance value.

Factors Affecting Resistance

• Material: Copper has lower resistance than nichrome.
• Thickness: Thicker wires have lower resistance.
• Length: Shorter wires have lower resistance.

Variable Resistor (Rheostat)

• A variable resistor allows for adjustable resistance in a circuit.

Electrical Circuits - Series

• Current flows along a single path.
• Current is the same at all points in the circuit.
• The total voltage is the sum of the voltages across each component.
• If the circuit is broken, no current flows.

Electrical Circuits - Parallel

• Current can flow along multiple paths.
• The total current equals the sum of the currents in the branches.
• The voltage across each branch is the same.
• If one branch is broken, current still flows in other branches.

Household Electricity

• Mains voltage in Hong Kong is 220 V.
• Electrical appliances convert electrical energy into other forms (e.g., heat, light, motion).
• Many appliances use the heating or magnetic effects of current.
• The three-pin plug has live, neutral, and earth wires.

Overloading and Short Circuits

• Overloading occurs when too many appliances use the same circuit. This can cause a circuit breaker or fuse to trip.
• Short circuits are low-resistance paths that dramatically increase current flow. This too can overheat and damage a circuit or cause a fire.

Fuses and Circuit Breakers

• Fuses and circuit breakers protect circuits from damage by interrupting current flow if it exceeds a safe level.

Power and Efficiency

• Electrical power is energy transferred in one second, measured in watts (W).
• Power rating is the power of an appliance when it operates at the indicated voltage.
• Efficiency is the percentage of input power that's converted to useful output power.
• Appliance labels indicate the efficiency rating of appliances.
• A kilowatt-hour (kWh) meter measures electrical energy usage.

Safety Precautions

• Use three-pin plugs to prevent electrical shocks.
• Use appropriate fuse ratings.
• Avoid overloading circuits, and check for damaged wiring.

Explore the fundamentals of electricity with this quiz on simple circuits. Learn about the components of circuits, circuit symbols, and the flow of electric current. Test your knowledge on how to create and understand circuit diagrams and the roles of conductors and insulators.