What are the necessary conditions for an electrical appliance to work?
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What are the necessary conditions for an electrical appliance to work?
What materials are considered electrical conductors and insulators?
| Meaning | Electrical conductors | Electrical insulators |
|---|---|---|
| Can conduct electricity | - all metals | - cotton |
| - graphite / pencil lead | - plastics | |
| (non-metal) | - wood | |
| - salt solution | - rubber | |
| - lemon juice | - wax | |
| - vinegar | - distilled water | |
| - alcohol |
What is the function of a switch in an electrical circuit?
A switch is used to open and close a circuit. The button is made of plastic to prevent electric shock.
What are the circuit symbols for a cell, battery, and switch?
| Circuit component | Circuit symbol |
|---|---|
| Cell / battery | [Vertical line with a short horizontal line on the left and a long horizontal line on the right.] |
| Battery | [Two vertical lines with alternating short and long horizontal lines on the left and right.] |
| Switch (open) | [A horizontal line with a circle in the middle and another horizontal line slightly above.] |
| Switch (closed) | [Two horizontal lines connected together with two circles on both lines.] |
What is the difference between a complete circuit and an incomplete circuit?
What is the energy conversion process in electrical appliances?
Chemical energy (stored in dry cells) → Electrical energy (flowing through the circuit) → Heat / light / sound energy (in light bulbs / electrical appliances)
What is the circuit symbol for an ammeter and a voltmeter?
| Circuit component | Circuit symbol |
|---|---|
| Ammeter | [A circle with the letter "A" inside and two horizontal lines on the left and right.] |
| Voltmeter | [A circle with the letter "V" inside and two horizontal lines on the left and right.] |
What is the definition of current in an electrical circuit?
Current is defined as a flow of electric charges.
What is the direction of current flow in a circuit?
The direction of current flow is from the positive terminal to the negative terminal.
What does an ammeter measure and what is its unit?
An ammeter measures the size of current, and its unit is ampere (A).
How does connecting more cells in a circuit affect the current and brightness of a bulb?
Connecting more cells results in a larger current, which makes the bulb brighter.
In the water flow model, what part of the circuit corresponds to the pump?
In the water flow model, the part of the circuit that corresponds to the pump is the cell.
What is the heating effect of current in a conductor?
The heating effect occurs when current passes through a conductor, and a larger current flowing results in a greater heating effect.
What is the energy conversion that occurs in devices like hairdryers and electric kettles?
The energy conversion in these devices is from electrical energy to thermal energy (and light or kinetic energy).
What is voltage and what does it measure?
Voltage is the measure of how much energy is supplied by the cell to the electric charges.
What does a voltmeter measure and what is its unit?
A voltmeter measures voltage, and its unit is volt (V).
What is resistance in an electrical circuit?
Resistance is the ability to oppose the flow of current.
What is a resistor and what is its unit?
A resistor is a component with a fixed value of resistance, and its unit is ohm (Ω).
How does larger resistance affect current and bulb brightness?
Larger resistance results in lower current flowing through, which makes the bulb dimmer.
What characterizes a series connection in a circuit?
In a series connection, there is one single path for current, the current is the same at different points, and the voltage of the energy source equals the sum of the voltage across each electrical appliance.
What happens to current flow if a series connection is broken at any point?
If a series connection is broken at any point, current will not flow.
What is the relationship between current in a parallel circuit and the branches?
The current flowing through the main loop is the sum of the electric current flowing through the branches.
How does resistance in a branch affect current in a parallel circuit?
A larger resistance in the branch results in a lower current flowing through that branch.
What is the voltage across each branch in a parallel connection?
The voltage across each branch is the same in a parallel connection.
What happens to other branches if one branch in a parallel circuit is open?
If one of the branches is open, the other branches will not be affected.
What is the mains voltage in Hong Kong?
The mains voltage in Hong Kong is 220V.
What are the three holes of a main socket and their functions?
The three holes of a main socket are:
What are the colors of the three wires in a three-pin plug?
The colors of the three wires are:
What occurs when too many appliances are connected to a mains socket?
When too many appliances are connected to a mains socket, they draw a large current and overloading occurs.
What is a short circuit and what causes it?
A short circuit occurs when there is a branch with a very low resistance for current to flow, leading to overheating of the circuit.
