IP Physics Notes (Upper Secondary, Year 3-4): 11) Current of Electricity

Study guide30 Sep 2025, 00:00 Z

Relate charge flow, potential difference, resistance, and I-V characteristics to core IP circuit analysis.

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Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 11) Current of Electricity cover?
A: Relate charge flow, potential difference, resistance, and I-V characteristics to core IP circuit analysis.

Quick recap - Electric current measures how quickly charge moves. Define the energy supplied (emf) and used (p.d.), then apply Ohm's law, resistivity relations, and characteristic curves to decode circuit behaviour.

The core idea is simple: Current is charge flow per second.

Use it as a working check: Link charge, current, time, voltage, resistance, and energy carefully. Use Ohm's law only when the component behaves ohmically at constant temperature.

Then go one layer deeper: Use the resistivity and I-V sections to practise identifying variables, reading graph shape, and explaining why metals, lamps, and diodes behave differently.

Keep your practice loop tight via our IP Physics tuition hub-it links each topic here to quizzes, diagnostics, and WA-style problem sets.

New to the Integrated Programme? Start with What is IP? | Browse all free IP notes.

These notes align with SEAB GCE O-Level Physics (6091) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Physics 6091 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for these notes.

Concept Map: What One Coulomb Does

Use this map before choosing a formula. It separates the flow question from the energy question.

cell or battery
  supplies energy to each coulomb
  emf = energy supplied per coulomb
        |
        v
charge moves around the circuit
  current = charge per second
        |
        v
component uses the energy
  p.d. = energy transferred per coulomb
        |
        v
resistance controls how much current flows for that p.d.

If the question gives time, start with charge flow: $Q = I t$

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

Question phrase	Quantity to find first	Formula lane	Unit check
"charge passing a point"	Charge moved	$Q = I t$	Time must be in seconds.
"energy transferred per coulomb"	Voltage or p.d.	$V = W / Q$	Joules per coulomb gives volts.
"opposition to current"	Resistance	$R = V / I$	Volts per ampere gives ohms.
"energy transferred by a component"	Work done or energy	$W = VQ$	Charge and voltage together give joules.

If the phrase says...	It is asking about...	Usual symbol
"energy supplied by the source per unit charge"	emf	$\mathcal{E}$
"energy converted in the component per unit charge"	p.d. across that component	$V$
"work done moving charge through the whole circuit"	source-side energy supply	$\mathcal{E}Q$
"work done in a resistor, lamp, or motor"	load-side energy transfer	$VQ$

Change made	What happens to resistance	Why
Same material, length doubled	Resistance doubles.	$R \propto L$ when $\rho$ and $A$ are unchanged.
Same material, cross-sectional area doubled	Resistance halves.	$R \propto 1 / A$ when $\rho$ and $L$ are unchanged.
Same material, diameter doubled	Resistance becomes one quarter as large.	Doubling diameter doubles radius, so area becomes four times as large.
Higher-resistivity material, same dimensions	Resistance increases in the same ratio as resistivity.	$\rho$ is the material factor in $R = \rho L / A$ .

Component	Graph	Key behaviour
Metal resistor	Straight line through origin	Constant $R$ ; obeys Ohm's law
Filament lamp	Curve flattening at higher $V$	Heating raises $R$ ; gradient decreases
Semiconductor diode	Nearly zero current reverse bias; sharp rise beyond threshold (~ $\pu{0.6 V}$ )	Conducts mainly in one direction

Graph cue	What it means physically	How to use resistance	Common trap
Straight line through the origin	Current is directly proportional to p.d. at constant temperature.	One constant value of $R = V / I$ works for the whole line.	Calling any straight line ohmic if it does not pass through the origin.
Filament lamp curve flattens as p.d. increases	The filament heats up, so its resistance increases.	Use $R = V / I$ at the stated point, or compare tangent steepness if the question asks about gradient.	Quoting one fixed resistance for the whole curve.
Diode current rises sharply in one direction only	The diode conducts mainly under forward bias after the threshold region.	Treat it as non-ohmic; use the graph reading at the stated voltage or current.	Applying Ohm's law as if the diode were a metal resistor.
Axes are swapped	The gradient may be $\Delta V / \Delta I$ or $\Delta I / \Delta V$ .	For a $V$ -against- $I$ graph, gradient is resistance. For an $I$

IP Physics Notes (Upper Secondary, Year 3-4): 11) Current of Electricity

Concept Map: What One Coulomb Does

Formula-choice checkpoint

Charge & Current

Worked Example: Charge Flow

Electromotive Force vs Potential Difference

Resistance & Ohm's Law

Worked Example: Calculating Resistivity

Resistivity variable-change checkpoint

I-V Characteristics to Memorise

I-V graph shape checkpoint

Worked Example: Reading a Graph Gradient

Practical Measurement Tips

Practice Quiz

Key Takeaways

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