Potential difference

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課程筆記

What is Potential Difference?

A battery or power supply gives energy to each charge in a circuit.
Electrical components (e.g., lamps, resistors) use this energy, transferring it to other stores.
Potential difference (voltage) measures the difference in energy that charges have between two points in a circuit.
Units: volts (V).
Measured by a voltmeter placed in parallel across the component.
Circuit symbol for a voltmeter: a circle with a V inside.

Potential Difference in Series Circuits

In a series circuit, the total potential difference is split across all components.
For two identical resistors in series, each gets half the total voltage (e.g., 5 V each from a 10 V cell).
The sum of potential differences across each component equals the total potential difference of the supply.

Potential Difference in Parallel Circuits

In a parallel circuit, each branch receives the full potential difference of the supply.
Potential difference across each parallel branch is the same (e.g., 10 V across each branch from a 10 V cell).
If a branch has multiple components in series, the voltage is shared among them (e.g., two bulbs in a branch each get 5 V).
A lamp with a higher potential difference across it glows brighter.

Advantages of Parallel Circuits for Lamps

Each lamp receives the full potential difference, so it is brighter than in series.
Lamps can be turned on and off independently if each branch has its own switch.
A circuit must be complete for current to flow.

Lamp Ratings

The lamp rating is the maximum potential difference that is safe to put across a lamp without breaking it.
Exceeding the rating can damage the lamp.

Series circuit: two identical resistors share the 10 V potential difference equally (5 V each).

Parallel circuit: each lamp receives the full 10 V potential difference.

Parallel branch with two bulbs in series: each bulb gets 5 V (half the branch voltage).

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練習題

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1.What is the unit of potential difference?
Easy
- AVolts
- BAmperes
- COhms
- DWatts
2.Which instrument is used to measure potential difference?
Easy
- AAmmeter
- BVoltmeter
- COhmmeter
- DGalvanometer
3.How is a voltmeter connected in a circuit?
Easy
- AIn series
- BIn parallel
- CEither series or parallel
- DNot connected
4.In a series circuit, how is the potential difference distributed?
Easy
- ASame across all components
- BSplit across components
- CZero across each component
- DEqual to the current
5.A 10 V cell is connected to two identical resistors in series. What is the potential difference across each resistor?
Medium
- A10 V
- B5 V
- C20 V
- D0 V
6.In a parallel circuit with a 10 V cell and two branches, what is the potential difference across each branch?
Easy
- A5 V
- B10 V
- C20 V
- D0 V
7.Which statement about lamps in parallel is correct?
Medium
- AEach lamp gets less than the full voltage
- BIf one lamp breaks, the others go out
- CEach lamp can be controlled independently with a switch
- DThe lamps are dimmer than in series
8.What does a lamp's rating indicate?
Easy
- AThe current it draws
- BThe maximum safe potential difference
- CThe resistance of the lamp
- DThe brightness of the lamp

更多題目

9.A circuit has a 12 V battery and three identical lamps in series. What is the potential difference across each lamp?
Medium
- A12 V
- B4 V
- C6 V
- D3 V
10.In a parallel circuit, the potential difference across each branch is 12 V. If one branch has two identical bulbs in series, what is the potential difference across each bulb?
Medium
- A12 V
- B6 V
- C24 V
- D0 V
11.Which of the following is true about potential difference?
Easy
- AIt is the same as current
- BIt is the energy per unit charge
- CIt is measured in amperes
- DIt is the resistance of a component
12.A voltmeter connected across a bulb reads 6 V. The bulb is then replaced by a resistor. What will the voltmeter read if the circuit is unchanged?
Medium
- A0 V
- B6 V
- CDepends on resistor value
- D12 V
13.Which statement about potential difference in a parallel circuit is correct?
Easy
- AThe potential difference across each branch is the same.
- BThe potential difference across each branch adds up to the total.
- CThe potential difference is lower in branches with more components.
- DThe potential difference is the same everywhere in the circuit.
14.What is the circuit symbol for a voltmeter?
Easy
- AA circle with a V inside
- BA circle with an A inside
- CA rectangle with a V inside
- DA zigzag line with a V above
15.A 12 V battery is connected to two resistors in series. The potential difference across one resistor is 8 V. What is the potential difference across the other resistor?
Medium
- A4 V
- B8 V
- C12 V
- D20 V
16.In the circuit shown, a 9 V battery is connected to two lamps in series. The voltmeter across lamp 1 reads 3 V. What does the voltmeter across lamp 2 read?
Medium
- A3 V
- B6 V
- C9 V
- D0 V
17.A circuit has a 6 V battery and two identical lamps in parallel. What is the potential difference across each lamp?
Easy
- A3 V
- B6 V
- C12 V
- D0 V
18.A 10 V battery is connected to a parallel circuit with two branches. One branch has a single resistor, the other branch has two identical resistors in series. What is the potential difference across each of the two series resistors?
Hard
- A5 V each
- B10 V each
- C2.5 V each
- D20 V each
19.A student measures the potential difference across a lamp as 4.5 V. The lamp is rated at 6 V. What does this mean?
Medium
- AThe lamp is safe and will not break.
- BThe lamp will be brighter than normal.
- CThe lamp will blow because the voltage is too high.
- DThe lamp will not light because the voltage is too low.
20.Which of the following is an advantage of lamps in parallel?
Easy
- AEach lamp is dimmer than in series.
- BLamps can be turned on and off independently.
- CThe circuit uses less current overall.
- DThe potential difference across each lamp is lower.
21.A voltmeter connected across a bulb reads 6 V. The bulb is replaced with a resistor of the same resistance. The circuit is unchanged. What will the voltmeter read?
Medium
- A6 V
- B0 V
- C3 V
- D12 V
22.A 12 V battery is connected to three lamps in series. The potential difference across lamp A is 4 V, across lamp B is 5 V. What is the potential difference across lamp C?
Medium
- A3 V
- B4 V
- C5 V
- D12 V
23.In the diagram, a 10 V battery is connected to two resistors in parallel. What is the reading on voltmeter V1?
Easy
- A10 V
- B5 V
- C0 V
- D20 V
24.A student wants to measure the potential difference across a lamp in a series circuit. How should the voltmeter be connected?
Easy
- AIn series with the lamp
- BIn parallel across the lamp
- CIn series with the battery
- DIn parallel across the battery
25.Which of the following is true about potential difference in a series circuit?
Easy
- AIt is the same across all components
- BIt is divided among the components
- CIt is zero across each component
- DIt is equal to the current times resistance
26.In the circuit shown, a 6 V battery is connected to two identical bulbs in series. A voltmeter connected across one bulb reads 3 V. What would a voltmeter read if connected across the other bulb?
Medium
- A0 V
- B3 V
- C6 V
- D12 V
27.A 12 V battery is connected to a parallel circuit with two branches. One branch has a single resistor, the other branch has two identical resistors in series. What is the potential difference across each of the two series resistors?
Hard
- A6 V each
- B12 V each
- C4 V each
- D3 V each
28.What is the correct circuit symbol for a voltmeter?
Easy
- AA circle with a V inside
- BA circle with an A inside
- CA zigzag line
- DA straight line
29.A lamp is rated at 12 V. What does this rating mean?
Easy
- AThe lamp will always have 12 V across it
- B12 V is the maximum safe potential difference for the lamp
- CThe lamp produces 12 V
- DThe lamp's resistance is 12 ohms
30.In a series circuit with a 9 V battery and three lamps, the potential difference across lamp A is 2 V and across lamp B is 3 V. What is the potential difference across lamp C?
Medium
- A4 V
- B5 V
- C6 V
- D14 V
31.Which of the following is an advantage of connecting lamps in parallel rather than in series?
Easy
- AEach lamp gets the same current
- BEach lamp gets the full battery voltage
- CThe circuit uses less total voltage
- DThe lamps are dimmer
32.A student sets up a circuit with a 10 V battery, a switch, and two lamps in series. The switch is open. What is the potential difference across the switch?
Medium
- A0 V
- B5 V
- C10 V
- D20 V
33.A voltmeter connected across a bulb in a circuit reads 6 V. The bulb is replaced by a resistor of the same resistance. The rest of the circuit is unchanged. What will the voltmeter read now?
Medium
- A0 V
- B3 V
- C6 V
- D12 V
34.In a parallel circuit with a 9 V battery, one branch has a 3 Ω resistor and the other branch has a 6 Ω resistor. What is the potential difference across the 6 Ω resistor?
Medium
- A3 V
- B6 V
- C9 V
- D18 V
35.Which statement about potential difference is correct?
Easy
- APotential difference is the same as current
- BPotential difference is measured in amperes
- CPotential difference is the energy transferred per unit charge
- DPotential difference is the resistance of a component
36.In a series circuit with a 12 V battery and three identical lamps, what is the potential difference across each lamp?
Medium
- A12 V
- B4 V
- C6 V
- D3 V
37.A circuit has a 12 V battery and two resistors in series. The potential difference across one resistor is 8 V. What is the potential difference across the other resistor?
Medium
- A4 V
- B8 V
- C12 V
- D20 V
38.Which of the following statements about potential difference in a parallel circuit is correct?
Easy
- AThe potential difference across each parallel branch is the same.
- BThe potential difference across each parallel branch adds up to the total.
- CThe potential difference is split equally among all components.
- DThe potential difference is zero across each branch.
39.A 12 V battery is connected to a series circuit with two resistors. The potential difference across one resistor is 7 V. What is the potential difference across the other resistor?
Medium
- A5 V
- B7 V
- C12 V
- D19 V
40.In the circuit shown, a 9 V battery is connected to two lamps in series. A voltmeter across lamp 1 reads 3 V. What does the voltmeter across lamp 2 read?
Medium
- A3 V
- B6 V
- C9 V
- D12 V
41.The potential difference across each parallel path is always the same.
Easy
True or false?
42.In a series circuit, potential difference is the same everywhere.
Easy
True or false?
43.The higher the potential difference across a lamp, the brighter the lamp.
Easy
True or false?
44.The lamp rating is the potential difference the lamp turns on at.
Easy
True or false?
45.Voltmeters go in series in a circuit.
Easy
True or false?
46.In a series circuit with a 12 V battery and two identical resistors, what is the potential difference across each resistor?
Medium
- A12 V
- B6 V
- C24 V
- D0 V
47.In a parallel circuit with a 9 V battery and two branches, what is the potential difference across each branch?
Easy
- A4.5 V
- B9 V
- C18 V
- D0 V
48.A lamp rated at 6 V can safely be connected to a 12 V supply.
Easy
True or false?
49.Which circuit symbol represents a voltmeter?
Easy
- AA circle with a V inside
- BA circle with an A inside
- CA zigzag line
- DA straight line with a dot
50.Match each circuit component with its correct description regarding potential difference.
Medium
- Voltmeter
- Resistor in series
- Lamp in parallel
- Battery
- Measures potential difference
- Potential difference splits across them
- Receives full potential difference
- Provides potential difference
51.State one advantage of having lamps in a parallel circuit.
Easy
52.A 12 V battery is connected to three identical lamps in series. What is the potential difference across each lamp?
Medium
53.A 12 V battery is connected to three identical lamps in series. What is the potential difference across each lamp?
Medium
- A4 V
- B3 V
- C6 V
- D5 V

複習筆記

## Potential Difference (Voltage) - **Definition**: Potential difference (p.d.) is a measure of the difference in energy that charges have between two points in a circuit. It is also called voltage. - **Unit**: Volts (V). - **Measurement**: Measured by a **voltmeter**, which is connected **in parallel** across the component. Circuit symbol: circle with "V". ### Key Rules - In a **series circuit**, p.d. is **split** across all components. For identical resistors, each gets an equal share. - In a **parallel circuit**, the p.d. across **each branch is the same** (equal to the source p.d.). - A p.d. drop only occurs when current passes through a component. ### Lamps and Brightness - Higher p.d. across a lamp makes it **brighter**. - **Lamp rating**: maximum safe p.d. for that lamp. ### Advantages of Parallel Circuits for Lamps 1. Each lamp receives the **full p.d.** (so brighter). 2. Lamps can be controlled **independently** with switches. ### Example - Cell of 10 V: In series with two identical resistors, each gets 5 V. In parallel, each branch gets 10 V.

Potential difference: A measure of the difference in energy that charges have between two points in a circuit. Also called voltage. Unit: volts (V).
Voltmeter: A device used to measure potential difference, connected in parallel across a component. Symbol: circle with 'V'.
Series circuit: A circuit where components are connected end-to-end; potential difference is split across components.
Parallel circuit: A circuit where components are connected across the same two points; potential difference across each branch is the same.
Lamp rating: The maximum potential difference that is safe to put across a lamp without it breaking.

字卡

What is potential difference?

Potential difference is a measure of the difference in energy that charges have between two points in a circuit.

What are the units of potential difference?

Volts (V).

What instrument measures potential difference?

A voltmeter.

How is a voltmeter connected in a circuit?

In parallel across the component being measured.

What is the circuit symbol for a voltmeter?

A circle with a 'V' inside.

When does a circuit experience a drop in potential difference?

When the current goes through an electrical component.

In a parallel circuit, what is the potential difference across each branch?

The same (equal to the source potential difference).

In a series circuit, how is potential difference distributed?

It is split across all components.

Two identical resistors in series across a 10 V cell: what is the potential difference across each?

5 V each (half of the total).

In a parallel circuit with two branches, one branch has a single lamp and the other has two identical lamps in series. The source is 10 V. What is the potential difference across the single lamp?

10 V.

In the same circuit, what is the potential difference across each of the two series lamps?

5 V each.

How does potential difference affect lamp brightness?

The higher the potential difference across a lamp, the brighter the lamp.

What is a lamp rating?

The maximum potential difference that is safe to put across a lamp without it breaking.

True or false: The potential difference across each parallel path is always the same.

True.

True or false: In a series circuit, potential difference is the same everywhere.

False. It is split across components.

True or false: The higher the potential difference across a lamp, the brighter the lamp.

True.

True or false: The lamp rating is the potential difference the lamp turns on at.

False. It is the maximum safe potential difference.

True or false: Voltmeters go in series in a circuit.

False. They go in parallel.

State one advantage of having lamps in a parallel circuit.

Each lamp receives the full potential difference and so is brighter. (Or: Each lamp can be turned on and off independently if there is a switch on each path.)

Draw the circuit symbol for a resistor.

A rectangle (or zigzag line, but typically a rectangle in KS3).

Draw the circuit symbol for a voltmeter.

A circle with a 'V' inside.

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