Electrical Quantities

Learn it by playing

Answer these questions to earn energy, then fish and explore. No account needed.

For teachers: ready-to-use lesson slides, revision notes, diagrams for Electrical Quantities (Co-ordinated Sciences (Double Award) [CIE], Physics) — use them in your lesson, or run the topic as a live class game.

Notes

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).

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).

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.

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**.

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.

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).

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.

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 $h = 3.6 \times$ 10⁶ J.
Cost of electricity = energy $(kW h) \times$ cost per unit.

A simple series circuit with a cell, switch, bulb, and ammeter.

Practice questions

Free preview — 8 of 24 questions. Sign up to see them all.

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.
Medium
4.Complete the sentence about conventional current.
Medium
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.
Hard
- 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:
Hard
- 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

Slides

Electric Charge

There are two types of electric charge: positive and negative.
Atoms contain positively charged protons, negatively charged electrons, and neutral neutrons.
Equal numbers of protons and electrons cancel out, so atoms are neutral overall.

What is the overall charge of an atom with 6 protons, 6 neutrons, and 6 electrons?

Positive
Negative
Neutral
Cannot tell

Attraction and Repulsion

Opposite charges attract; like charges repel.
A positive charge attracts a negative charge and repels another positive charge.
A negative charge attracts a positive charge and repels another negative charge.

Which of these are true?

Two positive charges attract each other.
A positive charge and a negative charge attract each other.
Two negative charges repel each other.

Charging by Friction

Rubbing two insulating materials together can transfer electrons from one to the other.
The material that gains electrons becomes negatively charged; the one that loses electrons becomes positively charged.
Only electrons move during charging by friction – positive charges do not move.

When a polythene rod is rubbed with a cloth, electrons are transferred $____ the$ rod, giving it $a ____$ charge.

Electric Fields (Extended)

An electric field is a region where an electric charge experiences a force.
The direction of the field at a point is the direction of the force on a positive charge.
Field lines point away from positive charges and toward negative charges.

What is the direction of the electric field at a point near a positive charge?

Towards the positive charge
Away from the positive charge
Circular around the charge
There is no field

Conductors and Insulators

Conductors (e.g., metals) allow charge to flow easily because they have delocalised electrons.
Insulators (e.g., plastic, rubber) do not have free charges and resist the flow of charge.
Semiconductors conduct under certain conditions, but are not required at this level.

Which of these are good electrical conductors?

Copper
Rubber
Aluminium
Glass

Electric Current

Current is the rate of flow of electric charge.
In metals, current is the flow of electrons.
Current is measured in amperes (A) using an ammeter connected in series.
Conventional current flows from positive to negative, opposite to electron flow.

Current is measured $in ____$ using $an ____$ connected $in ____$ .

Direct and Alternating Current

Direct current (d.c.) flows in one direction only, e.g., from a battery.
Alternating current (a.c.) changes direction periodically, e.g., mains electricity.
In the UK, mains a.c. has a frequency of 50 Hz and a voltage of about 230 V.

Which type of current is produced by a battery?

Alternating current
Direct current
Both
Neither

Voltage and Potential Difference

Voltage (potential difference) is the energy transferred per unit charge between two points.
It is measured in volts (V) using a voltmeter connected in parallel.
In a series circuit, the total voltage is shared among components.

How should a voltmeter be connected to measure the potential difference across a resistor?

In series with the resistor
In parallel with the resistor
In series with the power supply
It cannot be measured

Resistance and Ohm's Law

Resistance opposes the flow of current; it is measured in ohms (Ω).
Ohm's law: $V = I \times R$ , where V is voltage, I is current, R is resistance.
For an ohmic conductor at constant temperature, current is directly proportional to voltage.

Ohm's law states that the potential difference across a conductor is equal to $the ____$ multiplied by $the ____$ .

Investigating Resistance of a Wire

Resistance of a wire is directly proportional to its length.
Resistance is inversely proportional to its cross-sectional area (thickness).
The experiment uses a thin resistance wire, ammeter, voltmeter, and metre rule.

If the length of a wire is doubled, what happens to its resistance?

It halves
It stays the same
It doubles
It quadruples

Electrical Energy and Power

Electrical energy transferred: $E = V \times I \times t (joules)$ .
Power is the rate of energy transfer: $P = V \times I (watts)$ .
The kilowatt-hour (kWh) is a unit of energy used for household electricity bills.

The power of an appliance is calculated by multiplying $the ____ by$ $the ____$ .

Unlock all 24 questions, slides & more

Create a free account to see every question, the slides, flashcards and revision notes for this topic.

Past papers

Past-paper practice for this topic is coming soon.

🗂️ Coming soon