Electrical Quantities

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Electric Charge

There are two types of electric charge: positive and negative.
Inside an atom, electrons are negatively charged, protons are positively charged, and neutrons are neutral.
Atoms have equal numbers of protons and electrons, so overall they are neutral.
Like charges repel, opposite charges attract.
Electric charge is measured in coulombs (C) (Extended tier).

Structure of an atom showing protons, neutrons and electron shells.

Charging by Friction

Rubbing two insulating materials together transfers electrons from one to the other.
The material that gains electrons becomes negatively charged; the material that loses electrons becomes positively charged.
Example: rubbing a polythene rod with a cloth transfers electrons from the cloth to the rod → rod becomes negative, cloth becomes positive.
Example: rubbing an acetate rod with a cloth transfers electrons from the rod to the cloth → rod becomes positive, cloth becomes negative.
Only electrons move during charging by friction; protons do not move.

Apparatus for demonstrating charging by friction using a polythene rod and another insulating material.

Electric Fields (Extended Tier)

An electric field is a region where a charge experiences a force.
Field lines are directed from positive to negative charge.
Around a point charge, field lines are radial: outward for positive, inward for negative.
Between two parallel plates, the field is uniform with parallel, equally spaced lines.
Field lines are always perpendicular to the surface of a conductor.

Demonstration of a Van de Graaff generator with streamers and field lines around a charged sphere.

Conductors and Insulators

Conductors (e.g., metals) allow charge to flow easily because they have delocalised electrons.
Insulators (e.g., plastic, rubber, glass) have no free charges and do not allow charge to flow easily.
A gold-leaf electroscope can test conductivity: a good conductor makes the leaf fall quickly; an insulator makes it fall slowly or not at all.

A diagram showing delocalised electrons in a metal conductor.

Current

Electric current is the rate of flow of charge.
Current is measured in amperes (A) using an ammeter connected in series.
Conventional current flows from positive to negative terminal (opposite to electron flow).
Equation: I = \frac{Q}{t} , where Q is charge in coulombs, t is time in seconds (Extended tier).
In metals, current is a flow of negatively charged electrons.

A simple circuit showing current flow from a cell through a light bulb.

Direct and Alternating Current

Direct current (d.c.) flows in one direction only; produced by cells and batteries.
Alternating current (a.c.) changes direction periodically; produced by mains electricity (UK: 230 V, 50 Hz).
Graph of d.c. is a horizontal line; graph of a.c. is a sine wave.

Graph of alternating current

Electromotive Force and Potential Difference

Electromotive force (e.m.f.) is the energy supplied per unit charge by a source: E = \frac{W}{Q} (Extended tier).
Potential difference (p.d.) is the energy transferred per unit charge across a component: V = \frac{W}{Q} .
Both are measured in volts (V).
Voltmeter is connected in parallel to measure p.d.

A simple circuit labelled with the e.m.f. of the power supply.

Resistance and Ohm's Law

Resistance is the opposition to current; measured in ohms (Ω).
Ohm's law: R = \frac{V}{I} .
For a fixed resistor at constant temperature, current is directly proportional to voltage (ohmic conductor).
For a filament lamp, resistance increases with temperature (non-ohmic).
A diode allows current in one direction only (forward bias).

Current-voltage graphs for a resistor and a filament lamp.

Resistance of a Wire

Resistance is directly proportional to length: longer wire → higher resistance.
Resistance is inversely proportional to cross-sectional area: thicker wire → lower resistance.
Increasing temperature increases resistance due to more frequent collisions with vibrating metal ions.

Electrons moving through a material, colliding with atoms and increasing resistance.

Electrical Energy and Power

Electrical power P = VI , measured in watts (W).
Electrical energy E = VIt , measured in joules (J).
Alternative: P = I²R and P = \frac{V²}{R} .

Energy transfer in a washing machine and a toaster

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1.A polythene rod is rubbed with a cloth and becomes negatively charged. This happens because
Easy
- Aelectrons move from the cloth to the rod
- Belectrons move from the rod to the cloth
- Cprotons move from the cloth to the rod
- Dprotons move from the rod to the cloth
2.Which of the following is a good conductor of electricity?
Easy
- ARubber
- BPlastic
- CCopper
- DGlass
3.A lamp is rated at 12 V, 50 W. What is the current through the lamp when operating normally?
Medium
- A0.24 A
- B4.17 A
- C600 A
- D38 A
4.The resistance of a wire is 10 Ω. What is the potential difference across the wire when a current of 0.5 A flows through it?
Easy
- A0.05 V
- B5 V
- C20 V
- D10.5 V
5.A student connects a voltmeter to measure the potential difference across a lamp. How should the voltmeter be connected?
Easy
- AIn series with the lamp
- BIn parallel with the lamp
- CIn series with the power supply
- DIn parallel with the power supply
6.Which graph shows the current-voltage characteristic of a filament lamp?
Medium
- AA straight line through the origin
- BA curve that becomes less steep as voltage increases
- CA curve that becomes steeper as voltage increases
- DA horizontal line
7.A charge of 270 kC passes through a 12 V battery. How much electrical energy is transferred?
Medium
- A22.5 J
- B3.24 × 10⁶ J
- C3.24 × 10³ J
- D2.25 × 10⁴ J
8.Two identical resistors are connected in parallel. The total resistance is 2 Ω. What is the resistance of each resistor?
Medium
- A1 Ω
- B2 Ω
- C4 Ω
- D0.5 Ω

Thêm câu hỏi

9.What is the unit of electromotive force (e.m.f.)?
Easy
- AAmpere
- BVolt
- COhm
- DCoulomb
10.In the circuit shown, ammeter X reads 0.8 A. What is the reading on ammeter Y?
Medium
- A0 A
- B0.4 A
- C0.8 A
- D1.6 A
11.A wire of length L and cross-sectional area A has resistance R. What is the resistance of a wire of the same material with length 2L and cross-sectional area 3A?
Medium
- A(2/3)R
- B(3/2)R
- C6R
- D(1/6)R
12.A student charges a polythene rod by rubbing it with a cloth. The rod becomes negatively charged. Which statement explains how the rod becomes negatively charged?
Easy
- AThe rod gains electrons from the cloth.
- BThe rod loses electrons to the cloth.
- CThe rod gains protons from the cloth.
- DThe rod loses protons to the cloth.
13.The current in a lamp is 0.20 A and the potential difference across it is 6.0 V. What is the resistance of the lamp?
Easy
- A1.2 Ω
- B30 Ω
- C0.033 Ω
- D6.2 Ω
14.What is the unit of electric charge?
Easy
- AAmpere
- BCoulomb
- CVolt
- DOhm
15.A positively charged rod is brought near a suspended, charged balloon. The balloon is repelled. What is the charge on the balloon?
Easy
- APositive
- BNegative
- CNeutral
- DCannot be determined
16.What is the correct definition of electric current?
Easy
- AThe rate of flow of charge
- BThe energy transferred per unit charge
- CThe opposition to the flow of charge
- DThe force on a charged particle
17.Which component is used to measure potential difference?
Easy
- AAmmeter
- BVoltmeter
- COhmmeter
- DGalvanometer
18.A student uses a gold-leaf electroscope to test different materials. The electroscope is charged and the leaf rises. When a metal rod is touched to the plate, the leaf falls quickly. Which conclusion is correct?
Medium
- AMetal is a good conductor of electricity.
- BMetal is a good insulator of electricity.
- CMetal has no effect on the electroscope.
- DMetal causes the electroscope to gain more charge.
19.Which of the following is the correct definition of electric current?
Easy
- AThe rate of flow of electric charge
- BThe energy transferred per unit charge
- CThe opposition to the flow of charge
- DThe force that drives charge around a circuit
20.In an experiment to investigate how the resistance of a wire depends on its length, a student measures the potential difference across different lengths of the same wire while keeping the current constant. Which graph best shows the expected relationship between resistance R and length L?
Medium
- AA straight line through the origin with positive slope
- BA curve that flattens as L increases
- CA straight line with negative slope
- DA horizontal line
21.A student uses a gold-leaf electroscope to test whether a material is a conductor or an insulator. The electroscope is charged so that the leaf rises. When the material is touched to the plate, the leaf falls quickly. What does this indicate about the material?
Easy
- AIt is a good conductor.
- BIt is a good insulator.
- CIt is positively charged.
- DIt is negatively charged.
22.A student connects a variable resistor in series with a cell and a fixed resistor. The student measures the current and the potential difference across the fixed resistor. The variable resistor is adjusted to change the current. Which statement about the resistance of the fixed resistor is correct?
Medium
- AIt remains constant because the fixed resistor is ohmic.
- BIt increases as the current increases.
- CIt decreases as the current increases.
- DIt changes in proportion to the potential difference.
23.A student sets up a circuit with a cell, a switch, a lamp, and an ammeter in series. The ammeter reads 0.5 A. The student then adds a second identical lamp in series. What is the new reading on the ammeter?
Medium
- A0.25 A
- B0.5 A
- C1.0 A
- D0 A
24.In an experiment to measure the resistance of a wire, a student uses a circuit with a cell, an ammeter in series, and a voltmeter connected across the wire. The student records the following readings: current = 0.20 A, potential difference = 4.0 V. What is the resistance of the wire?
Easy
- A20 Ω
- B0.8 Ω
- C4.2 Ω
- D3.8 Ω
25.Which of the following is the correct way to connect a voltmeter to measure the potential difference across a lamp?
Easy
- AIn parallel with the lamp
- BIn series with the lamp
- CIn series with the cell
- DIn parallel with the ammeter
26.A student charges a gold-leaf electroscope by touching it with a negatively charged polythene rod. The leaf rises and stays risen. The student then brings a positively charged acetate rod close to the plate without touching it. What happens to the leaf?
Medium
- AIt rises further.
- BIt falls slightly.
- CIt stays at the same height.
- DIt falls completely.
27.A wire of length L and cross-sectional area A has resistance R. A second wire of the same material has length 2L and cross-sectional area A/2. What is the resistance of the second wire?
Medium
- A4R
- B2R
- CR
- DR/2
28.A student uses a circuit with a cell, a switch, a variable resistor, and a lamp in series. The student adjusts the variable resistor to increase the current. What happens to the brightness of the lamp and the potential difference across it?
Medium
- AThe lamp gets brighter and the potential difference increases.
- BThe lamp gets dimmer and the potential difference decreases.
- CThe lamp gets brighter and the potential difference decreases.
- DThe lamp gets dimmer and the potential difference increases.
29.In the circuit shown, a 12 V battery is connected to a 6 Ω resistor and a lamp in series. The current in the circuit is 1.5 A. What is the resistance of the lamp?
Medium
- A2 Ω
- B8 Ω
- C4 Ω
- D6 Ω
30.A student rubs a plastic rod with a cloth. The rod becomes positively charged. Which statement explains this?
Easy
- AElectrons move from the rod to the cloth.
- BElectrons move from the cloth to the rod.
- CProtons move from the rod to the cloth.
- DProtons move from the cloth to the rod.
31.Which particles move to cause a current in a copper wire?
Easy
- ACopper atoms
- BElectrons from the copper atoms
- CProtons from the copper nuclei
- DNeutrons from the copper nuclei
32.Like charges attract each other.
Easy
True or false?
33.Which of the following is a correct definition of potential difference?
Medium
- AThe rate of flow of electric charge
- BThe work done by a unit charge passing through a component
- CThe opposition to current
- DThe electrical work done by a source in moving a unit charge around a complete circuit
34.A voltmeter should be connected in series with the component being measured.
Easy
True or false?
35.A wire of length L and cross-sectional area A has resistance R. What is the resistance of a wire of the same material with length 2L and cross-sectional area 2A?
Medium
- AR
- B2R
- CR/2
- D4R
36.Which of the following materials is a good insulator?
Easy
- ASilver
- BCopper
- CRubber
- DAluminium
37.Match each component to its correct circuit symbol.
Medium
- Cell
- Lamp
- Resistor
- Ammeter
- A circle with a cross inside
- A rectangle
- Two parallel lines (long and short)
- A circle with an 'A' inside
38.Arrange the following steps in the correct order to measure the resistance of a wire using a voltmeter and ammeter.
Medium
- Connect the ammeter in series with the wire.
- Record the ammeter and voltmeter readings.
- Connect the voltmeter in parallel with the wire.
- Set up a circuit with a cell, switch, and wire.
39.Which of the following are correct statements about the gold-leaf electroscope? (Select all that apply)
Medium
- AThe leaf rises when a charged object is brought near the plate.
- BThe leaf stays risen after a charged object touches the plate and is removed.
- CThe leaf falls when a charged object touches the plate.
- DThe electroscope can be used to test if a material is a conductor or insulator.
- EThe leaf and stem are made of plastic.
40.Complete the sentence:
Easy
The unit of electric current is the ____.
41.A current of 0.5 A flows through a lamp for 2 minutes. Calculate the charge that flows through the lamp.
Easy
42.A current of 2.5 A flows through a lamp for 1 minute. Calculate the charge that flows through the lamp.
Easy
43.Complete the sentence using the words provided:
Medium
When a polythene rod is rubbed with a cloth, electrons are transferred from the ____ to the ____. The cloth becomes ____ charged and the rod becomes ____ charged.
44.Explain why a metal wire becomes hot when an electric current passes through it.
Medium
45.A current of 0.5 A flows through a lamp for 2 minutes. Calculate the charge that flows through the lamp.
Easy
- A72 C
- B54 C
- C66 C
- D60 C
46.A current of 2.5 A flows through a lamp for 1 minute. Calculate the charge that flows through the lamp.
Easy
- A180 C
- B165 C
- C150 C
- D135 C

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