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Questions and Answers
What is a potential consequence of overloading the mains circuit?
What is a potential consequence of overloading the mains circuit?
What happens during a short circuit related to the wire connected in parallel?
What happens during a short circuit related to the wire connected in parallel?
Why is it important to select a fuse with a rating slightly higher than the normal operating current?
Why is it important to select a fuse with a rating slightly higher than the normal operating current?
What is the primary function of a circuit breaker?
What is the primary function of a circuit breaker?
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How does the earth wire protect users from electric shock?
How does the earth wire protect users from electric shock?
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What happens to a fuse when the current passing through it exceeds its rating?
What happens to a fuse when the current passing through it exceeds its rating?
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What does a circuit breaker do once it has cut off the current due to an overload?
What does a circuit breaker do once it has cut off the current due to an overload?
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What occurs if the live wire of an appliance touches its metal case due to a loose connection?
What occurs if the live wire of an appliance touches its metal case due to a loose connection?
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What happens in a series circuit if it is broken at any point?
What happens in a series circuit if it is broken at any point?
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Which factor contributes to an increase in resistance in a wire?
Which factor contributes to an increase in resistance in a wire?
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What is the function of a variable resistor or rheostat in a circuit?
What is the function of a variable resistor or rheostat in a circuit?
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In a parallel circuit, how does the current behave in the branches?
In a parallel circuit, how does the current behave in the branches?
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How does the resistance of a copper wire compare to that of a nichrome wire of the same size?
How does the resistance of a copper wire compare to that of a nichrome wire of the same size?
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What is an example of a practical application of a variable resistor?
What is an example of a practical application of a variable resistor?
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What is true about the voltage across each branch in a parallel circuit?
What is true about the voltage across each branch in a parallel circuit?
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Which statement correctly describes electrical appliances?
Which statement correctly describes electrical appliances?
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What effect do electric motors utilize in household appliances?
What effect do electric motors utilize in household appliances?
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What happens to the current when multiple electrical appliances are connected to a single mains socket?
What happens to the current when multiple electrical appliances are connected to a single mains socket?
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Which wire in a three-pin plug is required for safety, helping to prevent electric shocks?
Which wire in a three-pin plug is required for safety, helping to prevent electric shocks?
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In a domestic electrical circuit, what is the connection method used for sockets?
In a domestic electrical circuit, what is the connection method used for sockets?
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What is the main purpose of a fuse in an electrical circuit?
What is the main purpose of a fuse in an electrical circuit?
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Which type of energy is predominantly converted to thermal energy by the heating elements of appliances?
Which type of energy is predominantly converted to thermal energy by the heating elements of appliances?
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Why might a circuit breaker be preferred over a fuse in household circuits?
Why might a circuit breaker be preferred over a fuse in household circuits?
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What is a potential risk if the earth wire is not properly connected in an appliance?
What is a potential risk if the earth wire is not properly connected in an appliance?
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Study Notes
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.
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Description
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.
