Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want electrical quantities — charge, current, voltage and resistance — to become a reliable source of marks instead of a tangle of units and symbols.
What query it owns: how to understand and revise electrical quantities in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the electrical quantities revision-guide angle, while Tutopiya’s Electrical Quantities subtopic page owns the learning resource and the free Electrical Quantities quiz owns the practice.

Electrical quantities describe how charge flows in a circuit. Cambridge IGCSE Coordinated Science (0654) expects you to define current, voltage and resistance, use V = IR (Ohm’s law), and know that Q = It links charge, current and time. This guide links each quantity to the calculation and explanation questions examiners set.

Key takeaways

• Electric current is the rate of flow of charge: I = Q/t (unit: ampere, A).
• Potential difference (voltage) is energy per unit charge: V = E/Q (unit: volt, V).
• Resistance opposes current flow (unit: ohm, Ω).
• Ohm’s law: V = IR (for an ohmic conductor at constant temperature).
• Ammeter in series; voltmeter in parallel.

What are electrical quantities in Cambridge IGCSE Coordinated Science?

Current measures how much charge passes a point each second. Voltage (p.d.) measures the energy transferred per coulomb of charge between two points. Resistance measures how much a component opposes current. These three quantities are linked by Ohm’s law and are measured with ammeters and voltmeters connected correctly in a circuit.

You can read the full explanation, diagrams and notes on Tutopiya’s Electrical Quantities subtopic page before you attempt questions.

Key quantities and equations

Quantity	Symbol	Unit	Equation
Charge	Q	coulomb (C)	Q = It
Current	I	ampere (A)	I = Q/t
Potential difference	V	volt (V)	V = IR
Resistance	R	ohm (Ω)	R = V/I
Energy transferred	E	joule (J)	E = VIt

Example: 2 A for 30 s → Q = 2 × 30 = 60 C.

Electrical quantities in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical electrical quantities stem
Define	Precise scientific meaning	”Define electric current.”
Calculate	Use V = IR or Q = It	”Calculate the resistance of the lamp.”
State	Give a fact or unit	”State the unit of potential difference.”
Explain	Link cause and effect	”Explain why an ammeter must be connected in series.”

Worked exam-style stems (how to answer the wording)

1. “A current of 0.5 A flows for 2 minutes. Calculate the charge that passes.” t = 120 s → Q = It = 0.5 × 120 = 60 C. Mark-scheme reward: time converted to seconds + correct substitution.
2. “The p.d. across a resistor is 12 V and the current is 3 A. Calculate the resistance.” R = V/I = 12/3 = 4 Ω. Reward: correct rearrangement and unit.
3. “Define potential difference between two points in a circuit.” The energy transferred per unit charge passing between the two points. Reward: energy per unit charge.

Test yourself with the Electrical Quantities quiz once you can define each quantity, use V = IR and connect meters correctly.

How electrical quantities connect to the rest of Coordinated Science physics

Electrical quantities build on Simple Phenomena of Magnetism and lead into Circuit Diagrams and Series And Parallel Circuits. The Cambridge IGCSE Coordinated Science resource hub links every Electricity And Magnetism subtopic.

Common mistakes students make

• Connecting an ammeter in parallel (it must be in series).
• Connecting a voltmeter in series (it must be in parallel).
• Forgetting to convert minutes to seconds in Q = It calculations.
• Confusing current (rate of flow) with charge (total amount).
• Using V = IR for a filament lamp at changing temperature without noting non-ohmic behaviour.

When you need more support

If electrical quantity questions keep costing marks, work through the Electrical Quantities quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Are electrical quantities hard in Coordinated Science? Learn the four key definitions, V = IR and Q = It, plus how to connect ammeters and voltmeters — that covers most questions.

What is Ohm’s law? For an ohmic conductor at constant temperature, potential difference is directly proportional to current: V = IR.

What is the difference between current and charge? Current (A) is the rate of flow of charge; charge (C) is the total amount of electricity that has passed.

How do I revise electrical quantities effectively? Practise definitions, V = IR and Q = It calculations, and meter connections, then take the Electrical Quantities quiz.

Ready to master Cambridge IGCSE Coordinated Science electrical quantities?

Start with the Electrical Quantities subtopic page, then book a free trial with a Cambridge IGCSE Coordinated Science specialist to turn electrical knowledge into guaranteed marks.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial