Electrical Quantities

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Notas de aula

Electric Charge

There are two types of electric charge: positive and negative.
Like charges repel, opposite charges attract.
Charge is measured in coulombs (C) (Extended Tier).

Structure of an atom

Charging by Friction

Rubbing two insulators together transfers electrons from one to the other.
The material that gains electrons becomes negatively charged; the one that loses electrons becomes positively charged.
A charged object can attract uncharged objects (e.g., comb picking up paper).

Transfer of electrons between charged insulators

Electric Fields (Extended Tier)

An electric field is a region where a charge experiences a force.
Field direction is the direction of force on a positive test charge.
Field lines point from positive to negative charges.

Electric field around a positive point charge

Electrical Conductors & Insulators

Conductors (e.g., metals) have free electrons that can move, allowing charge to flow.
Insulators (e.g., plastic, rubber) have no free charges and do not conduct easily.
Metals conduct well because of their delocalised electrons.

Metallic lattice structure

Current

Electric current is the rate of flow of charge: I = \frac{Q}{t} .
Current is measured in amperes (A) using an ammeter connected in series.
Conventional current flows from positive to negative; electron flow is opposite.
Direct current (d.c.) flows in one direction; alternating current (a.c.) changes direction periodically.

A simple series circuit

Voltage (Potential Difference)

Voltage (or potential difference) is the energy transferred per unit charge.
Measured in volts (V) using a voltmeter connected in parallel.
In a series circuit, the total voltage is shared among components.
Electromotive force (e.m.f.) is the voltage supplied by a source (Extended Tier).

Potential difference shared in a series circuit

Resistance

Resistance opposes current: R = \frac{V}{I} , measured in ohms (Ω).
Resistance is directly proportional to length and inversely proportional to cross-sectional area.
Ohmic conductors have constant resistance (linear I–V graph); non-ohmic have variable resistance.
Increasing temperature increases resistance due to more frequent collisions with metal ions.

The effect of resistance on current

Electrical Energy & Power

Electrical energy transferred: E = VIt , measured in joules (J).
Power is the rate of energy transfer: P = IV = \frac{E}{t} , measured in watts (W).
Domestic energy is often measured in kilowatt-hours (kW h): 1 kW h = 3.6 × 10⁶ J.
Cost of electricity = energy (kW h) × cost per unit.

Energy transfer in an electrical circuit

Slides

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CADASTRE-SE — GRÁTIS ENTRAR

Questões de prática

Prévia grátis — 8 de 56 perguntas. Cadastre-se para ver todas.

1.Which two particles in an atom have equal and opposite charges?
Easy
- Aproton and neutron
- Bproton and electron
- Cneutron and electron
- Dproton and proton
2.Like charges attract each other.
Easy
True or false?
3.State the name of the instrument used to measure electric current.
Easy
4.Complete the sentence about conventional current.
Easy
Conventional current flows from the ____ terminal to the ____ terminal of a cell.
5.A charge of 4 C passes a point in 0.5 s. What is the current in amperes?
Medium
- A7
- B9
- C10
- D8
6.Match each type of current to its description.
Medium
- Direct current (d.c.)
- Alternating current (a.c.)
- Continuously changes direction
- Steady current in one direction
7.A 12 Ω resistor has a current of 0.3 A flowing through it. What is the potential difference across the resistor?
Medium
- A3.6 V
- B12.3 V
- C0.025 V
- D40 V
8.Arrange the following steps in the correct order to investigate how the length of a wire affects resistance:
Medium
- Record potential difference and current
- Set up circuit with clips 10 cm apart
- Move clips further apart in 10 cm intervals
- Repeat until clips are 1 m apart

Mais perguntas

9.A washing machine runs for 3 hours 16 minutes at 230 V with a current of 10.0 A. Calculate the energy transferred in MJ.
Hard
- A27
- B30
- C24
- D33
10.Which of the following is a good conductor of electricity?
Easy
- Arubber
- Bplastic
- Ccopper
- Dglass
11.State the unit of electromotive force (e.m.f.).
Easy
12.In a series circuit, the sum of the voltages across each component equals the total voltage of the power supply.
Easy
True or false?
13.Match each electrical quantity to its correct unit.
Easy
- Current
- Potential difference
- Resistance
- Volt (V)
- Ampere (A)
- Ohm (Ω)
14.A 60 W light bulb is left on for 6 hours. Calculate the energy transferred in kilowatt-hours.
Medium
- A-0.64
- B0.36
- C2.36
- D1.36
15.Complete the sentence about resistance.
Medium
The resistance of a wire is directly proportional to its ____ and inversely proportional to its ____.
16.Arrange the following materials in order of increasing electrical conductivity (lowest first):
Medium
- glass
- silver
- plastic
- copper
17.Name the type of current produced by a battery.
Easy
18.Which graph shows the I-V characteristic of an ohmic conductor?
Medium
- AA straight line through the origin
- BA curve that flattens off
- CA line that does not pass through the origin
- DA curve that bends upwards
19.An ammeter is connected in parallel with a component to measure the current through it.
Easy
True or false?
20.A cooker transfers 1.2 × 10⁹ J of energy in a year. If 1 kWh costs 14.2 p, calculate the cost in pounds (£).
Hard
- A56.79
- B47.33
- C42.6
- D52.06
21.Complete the sentence about the kilowatt-hour.
Easy
1 kilowatt-hour is equal to ____ joules.
22.Match each component to its circuit symbol description.
Medium
- Cell
- Ammeter
- Voltmeter
- Connected in series
- Connected in parallel
- Provides e.m.f.
23.Arrange the following steps in the correct order to charge an insulator by friction:
Medium
- Electrons transfer from one material to the other
- Rub two insulating materials together
- One material becomes positively charged, the other negatively charged
24.State the name of the law that relates current, voltage and resistance.
Easy
25.Which of the following is a correct description of the charge on a proton?
Easy
- Apositive
- Bnegative
- Cneutral
- Dalternating
26.Opposite charges attract each other.
Easy
True or false?
27.Which of the following materials is a good conductor of electricity?
Easy
- ARubber
- BCopper
- CPlastic
- DWood
28.A voltmeter is connected in series with a component to measure the potential difference across it.
Easy
True or false?
29.Which of the following is the correct definition of electromotive force (e.m.f.)?
Medium
- AThe energy transferred per unit charge by a power supply
- BThe opposition to current in a circuit
- CThe rate of flow of electric charge
- DThe work done per unit charge between two points in a circuit
30.Arrange the following steps in the correct order to investigate how the length of a wire affects resistance.
Medium
- Measure the current and voltage for a 10 cm length of wire
- Set up the circuit with crocodile clips at 10 cm apart on the resistance wire
- Calculate the resistance using R = V/I
- Repeat for different lengths up to 1 m
31.A 60 W light bulb is left on for 6 hours. How much energy is transferred in kilowatt-hours?
Medium
- A0.36 kWh
- B3.6 kWh
- C360 kWh
- D10 kWh
32.A polythene rod is rubbed with a cloth and becomes negatively charged. What happens to the cloth?
Medium
- AIt becomes positively charged because it gains protons.
- BIt becomes positively charged because it loses electrons.
- CIt becomes negatively charged because it gains electrons.
- DIt remains neutral because charge is destroyed.
33.Which of the following are correct statements about electric charge? (Select all that apply)
Medium
- ALike charges attract each other.
- BOpposite charges attract each other.
- CA neutral object has no charge at all.
- DCharge is measured in coulombs.
- EElectrons are positively charged.
34.An ammeter must be connected in parallel with a component to measure the current through it.
Easy
True or false?
35.A 12 V battery is connected to a 6 Ω resistor. What is the power dissipated by the resistor?
Medium
- A2 W
- B24 W
- C72 W
- D144 W
36.A student investigates how the length of a resistance wire affects its resistance. Which graph shows the expected relationship between resistance and length?
Medium
- AA straight line through the origin with positive gradient
- BA curve that flattens as length increases
- CA straight line with negative gradient
- DA horizontal line
37.In a series circuit, the voltage across each component is always the same.
Easy
True or false?
38.A 12 V battery is connected to a circuit. A charge of 4 C passes through the battery. How much energy is transferred to the charge by the battery?
Medium
- A48 J
- B3 J
- C0.33 J
- D12 J
39.Which of the following are correct statements about conventional current? (Select all that apply)
Medium
- AIt flows from positive to negative terminal of a cell.
- BIt is in the same direction as electron flow.
- CIt is defined as the flow of positive charge.
- DIt is measured in amperes.
40.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 A/2?
Hard
- A4R
- B2R
- CR
- DR/2
41.Arrange the following steps in the correct order to measure the resistance of a wire using a voltmeter and ammeter.
Medium
- Connect the voltmeter in parallel with the wire.
- Record the voltmeter and ammeter readings.
- Set up the circuit with an ammeter in series and a power supply.
- Calculate resistance using R = V/I.
42.Which of the following materials is an electrical insulator?
Easy
- ACopper
- BSilver
- CPlastic
- DSteel
43.In the experiment to investigate how the length of a wire affects its resistance, which variable is the independent variable?
Easy
- AResistance
- BLength of the wire
- CCurrent through the wire
- DVoltage across the wire
44.A student investigates how the length of a wire affects its resistance. They obtain the following results: length = 0.20 m, resistance = 1.5 Ω; length = 0.40 m, resistance = 3.0 Ω; length = 0.60 m, resistance = 4.5 Ω. Which graph best represents the relationship between resistance and length?
Medium
- AA straight line through the origin with positive slope
- BA curve that flattens as length increases
- CA straight line with negative slope
- DA horizontal straight line
45.Which of the following are correct safety precautions when carrying out the experiment to investigate how the length of a wire affects its resistance? (Select all that apply)
Medium
- AUse low currents to keep the wire cool
- BTouch the wire to check its temperature
- CSwitch off the power supply if you smell burning
- DKeep liquids away from the electrical equipment
46.In the experiment to investigate how the length of a wire affects its resistance, the resistance is directly proportional to the length of the wire.
Easy
True or false?
47.Complete the sentence.
Easy
When a plastic rod is rubbed with a cloth, electrons are transferred from the ____ to the ____.
48.A charge of 6 C flows through a component in 2 seconds. What is the current in amperes?
Easy
49.A charge of 12 C flows through a component in 3 seconds. What is the current in amperes?
Easy
50.A current of 2.5 A flows through a resistor for 30 seconds. Calculate the charge that passes through the resistor.
Easy
51.State what is meant by an electric field.
Easy
52.Explain why a negatively charged polythene rod can attract small pieces of uncharged paper.
Medium
53.Explain why the wire becomes hot when a large current passes through it in the experiment to investigate resistance.
Medium
54.A charge of 6 C flows through a component in 2 seconds. What is the current in amperes?
Easy
- A2 A
- B5 A
- C3 A
- D4 A
55.A charge of 12 C flows through a component in 3 seconds. What is the current in amperes?
Easy
- A4 A
- B6 A
- C5 A
- D3 A
56.A current of 2.5 A flows through a resistor for 30 seconds. Calculate the charge that passes through the resistor.
Easy
- A83 C
- B67 C
- C75 C
- D91 C

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