Understanding Physics: Electricity: Edexcel IGCSE Science Single Award Explained

Electricity is one of those topics that clicks once you stop thinking of it as abstract and start thinking of it as plumbing for charge

Every time you switch on a lamp, charge a phone or use a kettle, you are relying on the physics covered in this section. The electricity content of the Pearson Edexcel IGCSE Science Single Award (4SS0) introduces the core concepts of current, voltage, resistance and power, and asks you to apply them to practical circuits. It is one of the more calculation-rich parts of the physics paper, and the good news is that the calculations follow predictable patterns.

These edexcel igcse science single award revision notes cover every specification point in the electricity section: units, mains electricity, and current and voltage in circuits. You will find the key equations, worked examples, and the mistakes that trip students up most often. Use these as your edexcel igcse science single award notes for focused revision, and follow up with past paper practice.

Units

The electricity section uses the following units, and you need to be comfortable with all of them:

Mains electricity

The specification covers two concepts in this topic:

Power, current and voltage: The relationship is P = I x V, where P is power in watts, I is current in amperes, and V is voltage in volts. This equation tells you how much energy is transferred per second.

Alternating current (a.c.) versus direct current (d.c.): Mains electricity is alternating current, meaning the direction of current flow reverses many times per second. In the UK, the mains frequency is 50 Hz. A cell or battery supplies direct current, where the current flows in one direction only. This distinction matters because some devices require a.c. (such as transformers) while others require d.c. (such as electronic circuits).

Current and voltage in circuits

Current in a series circuit

In a series circuit, the current is the same at every point. If you measure the current before a lamp and after a lamp, the readings will be identical. This is because the same charge flows through every component in sequence. Adding more components (such as more lamps) to a series circuit increases the total resistance, which reduces the current for a given voltage.

Current-voltage characteristics

The specification asks you to describe how current varies with voltage in three types of component:

• Wire (or fixed resistor): The current is directly proportional to the voltage. The graph is a straight line through the origin, and the resistance stays constant. This is Ohm's law behaviour.
• Metal filament lamp: At low voltages, the graph is roughly straight. As the voltage increases, the filament heats up, its resistance increases, and the graph curves, becoming less steep. The lamp does not obey Ohm's law because its resistance changes with temperature.

You should be able to describe the experimental setup for investigating these characteristics: connect the component in series with an ammeter and a variable resistor (or variable power supply), with a voltmeter connected in parallel across the component. Vary the voltage, record the current, and plot I-V graphs.

Lamps and LEDs can be used to indicate the presence of a current in a circuit. An LED (light-emitting diode) lights up when current flows through it in the correct direction, making it useful as a current indicator.

Ohm's law: V = IR

This is the central equation of the electricity section:

V = I x R

where V is voltage (potential difference) in volts, I is current in amperes, and R is resistance in ohms.

You can rearrange this to find any of the three quantities: I = V / R, or R = V / I.

Changing the resistance in a circuit affects the current. If you increase the resistance and keep the voltage the same, the current decreases. If you decrease the resistance, the current increases. This qualitative understanding is just as important as the calculation.

What current actually is

Current is the rate of flow of charge. In solid metallic conductors, the electric current is a flow of negatively charged electrons. These electrons move from the negative terminal of the battery, through the circuit, to the positive terminal. (Conventional current, used in circuit diagrams, runs the opposite way, from positive to negative, but the actual electron flow is negative to positive.)

Resistors in series

When two resistive components are connected in series, the total resistance is the sum of their individual resistances:

R_total = R₁ + R₂

The current through both is the same (series circuit rule), and the voltage splits across them in proportion to their resistances.

Common mistakes in electricity

• Confusing series and parallel: In series, current is the same everywhere and voltages add up. In parallel, voltage is the same across each branch and currents add up. The specification for this single award focuses on series circuits, but knowing the distinction helps you avoid errors.
• Forgetting to convert units: If a question gives resistance in kilohms (k ohms), convert to ohms before using V = IR. 1 k ohm = 1000 ohms.
• Mixing up current direction: Conventional current flows from positive to negative. Electron flow is from negative to positive. The exam may test either, so read the question carefully.
• Missing the distinction between a.c. and d.c.: Mains = a.c. Battery = d.c. A short, clear statement is all that is needed.

Self-check questions

1. A toaster draws a current of 4 A from a 230 V supply. Calculate its power.
2. State the difference between alternating current and direct current.
3. A current of 0.3 A flows through a 50 ohm resistor. Calculate the voltage across it.
4. Describe how you would investigate the current-voltage characteristics of a filament lamp.
5. Two resistors, 15 ohms and 25 ohms, are connected in series to a 12 V battery. Calculate the current flowing and the voltage across each resistor.
6. Explain why the current decreases when more lamps are added in series to a circuit.
7. What is the direction of electron flow in a metallic conductor?
8. A 60 W lamp operates at 12 V. Calculate the current it draws.

Electricity in the context of the single award

The physics: electricity edexcel igcse section carries three equations (P = IV, V = IR, and R_total = R₁ + R₂) that between them cover most of the marks available. If you can rearrange each one confidently and apply it to simple circuit problems, you are well placed. The descriptive content (a.c. vs d.c., electron flow, I-V characteristics) is equally important but requires recall rather than calculation.

For your igcse 4ss0 physics: electricity revision, practise the calculations until they are automatic, and make sure you can sketch the I-V graphs for a wire and a filament lamp from memory. These are the areas where marks are most predictable in the edexcel igcse exam.

Self-check questions

1. State two differences between the structure of a plant cell and an animal cell.
2. Describe the process of osmosis and explain why it is important in living organisms.
3. Explain the difference between an exothermic and an endothermic reaction, giving one example of each.
4. A car accelerates from rest to 20 m/s in 5 seconds. Calculate its acceleration and the resultant force if the car has a mass of 1200 kg.
5. Describe the structure of an atom, naming each subatomic particle and stating its relative charge and mass.

Self-check questions

1. State two differences between a chemical change and a physical change, giving one example of each.
2. Explain why a thermometer placed in a beaker of melting ice reads 0 degrees for several minutes even though heat is being supplied.
3. A student measures the voltage across a resistor as 6 V and the current through it as 0.5 A. Calculate the resistance and state the unit.
4. Describe how the structure of the small intestine is adapted for the efficient absorption of digested food molecules.

These edexcel igcse science single award notes are your starting point. Follow them with edexcel igcse science single award practice questions from past papers to see how the concepts are tested in context. The edexcel igcse science single award explained approach gives you the framework; the exam rewards its application. The Green Bridge CBT platform offers electricity questions organised by specification point, so you can target your weakest areas and measure your improvement before the exam.