Who this is for: Cambridge IGCSE Physics (0625) students who want electrical quantities — current, voltage, resistance and power — to become reliable marks instead of symbols detached from what the circuit is doing.
What query it owns: how to understand and revise electrical quantities in Cambridge IGCSE Physics.
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 quiz owns the practice.

Electrical quantities are the foundation of every electricity question in Cambridge IGCSE Physics (0625). Examiners expect you to define charge, current, e.m.f., potential difference and resistance, apply V = IR and P = VI, and interpret I–V graphs for resistors, lamps and diodes. This guide covers the syllabus content and the question types that appear every year.

Key takeaways

• Current (I) = charge per second: I = Q/t (unit: ampere, A).
• Potential difference (V) = energy per unit charge: V = W/Q (unit: volt, V).
• Resistance (R) = V/I (unit: ohm, Ω); Ohm’s law: V = IR for ohmic conductors at constant temperature.
• Power P = VI; energy E = VIt (or E = Pt).
• Series: same current; resistances add. Parallel: same p.d. across branches; 1/R = 1/R₁ + 1/R₂.

What are electrical quantities in Cambridge IGCSE Physics?

Electrical quantities describe how charge flows and how energy is transferred in a circuit. Current is the rate of flow of charge; potential difference is the energy transferred per coulomb of charge; resistance opposes current. In Cambridge IGCSE Physics (0625) you must also distinguish e.m.f. (energy supplied per coulomb by a source) from p.d. (energy transferred per coulomb across a component).

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

The core ideas you must master

Idea	What it means	How the exam uses it
I = Q/t	Current is coulombs per second	”Calculate the charge passing in 2 minutes.”
V = IR	Ohm’s law	”Calculate the resistance of the resistor.”
P = VI	Electrical power	”Calculate the power of the heater.”
Series resistance	R_total = R₁ + R₂ + …	”Find the total resistance.”
Parallel resistance	1/R = 1/R₁ + 1/R₂	”Calculate the combined resistance.”

Series vs parallel: which rule applies?

Quantity	Series circuit	Parallel circuit
Current	Same through all components	Splits between branches; adds at junctions
Potential difference	Shared across components; adds to source p.d.	Same across each parallel branch
Resistance	R_total = sum of resistances	Combined R is less than smallest branch
If one lamp fails (break)	Whole circuit off	Other branches may still work

How to solve electrical calculation questions — step by step

1. Sketch the circuit and label known values (V, I, R, P, t).
2. Choose the correct formula — V = IR, P = VI, E = VIt, or series/parallel rules.
3. Convert units — mA to A, kΩ to Ω, minutes to seconds.
4. Substitute and calculate; include units in the final answer.
5. Check reasonableness — parallel resistance must be less than any single resistor.

Once you have worked through a few, test yourself with the free Electrical Quantities quiz.

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

Command word / phrase	What the question wants	Typical electricity stem
Define	Precise syllabus definition	”Define electric current.”
Calculate	Show formula and working	”Calculate the power dissipated.”
Sketch	I–V graph shape	”Sketch the I–V graph for a filament lamp.”
Explain	Cause and effect	”Explain why resistance increases as the lamp heats up.”
State	Short factual answer	”State the unit of resistance.”

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 conversion + Q = It.
2. “A resistor has resistance 12 Ω and p.d. 6 V across it. Calculate the current.” I = V/R = 6/12 = 0.5 A. Reward: Ohm’s law rearrangement.
3. “A 60 W lamp is connected to 240 V. Calculate the current in the lamp.” I = P/V = 60/240 = 0.25 A. Reward: P = VI rearranged to I = P/V.

When you can recognise the wording instantly, work through the Electrical Quantities quiz to lock the formulas in.

How electrical quantities connect to the rest of the syllabus

Quantities feed directly into Electric Circuits — circuit building, LDRs and thermistors. Electrical Safety uses current and power to explain fuse ratings. The Cambridge IGCSE Physics resource hub links every Electricity and Magnetism subtopic.

Common mistakes students make

• Confusing current with potential difference (current is flow; p.d. drives flow).
• Using V = IR for a lamp without noting resistance changes with temperature.
• Adding parallel resistances directly instead of using 1/R = 1/R₁ + 1/R₂.
• Forgetting to convert mA to A or minutes to seconds.
• Stating power in watts but calculating with joules and seconds inconsistently.

When you need more support

If Ohm’s law and power calculations keep costing marks, work through the Electrical Quantities quiz, then get focused help from a Cambridge IGCSE Physics tutor.

Frequently asked questions

Is electricity hard in Cambridge IGCSE Physics? The formulas are few, but marks are lost when students confuse series and parallel rules or mix up units.

What is the difference between e.m.f. and p.d.? E.m.f. is energy supplied per coulomb by the source; p.d. is energy transferred per coulomb across a component.

Why does a lamp not obey Ohm’s law at all temperatures? Filament temperature rises with current → resistance increases → I–V graph is curved, not through origin.

How do I revise electrical quantities effectively? Learn each formula with units, practise series and parallel combinations, sketch I–V graphs, then take the Electrical Quantities quiz.

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