IB Physics Electric Circuits: Current, Voltage, Resistance

Electric circuits in IB Physics are not just formula substitution. The same equation can appear in a calculation question, an explanation question, or a graph question, and each one needs a slightly different answer.

This guide keeps the focus on current, voltage, and resistance as physical ideas, not just letters in an equation.

Quick Answer

For IB Physics electric circuits, keep the model visible:

• Current is the rate of flow of charge.
• Potential difference is energy transferred per unit charge.
• Resistance opposes current and links voltage to current through V = IR.
• Series and parallel circuits distribute current and voltage differently.
• Power questions often need P = IV or related substitutions.
• Explanation answers should describe what happens to charge or energy, not only quote an equation.

Turn Formula Knowledge Into IB Explanation

IB circuit questions often ask for a calculation and then an explanation. The explanation needs physics language, not only the equation.

If the command term is explain, write a cause-and-effect sentence. For example: increasing resistance at constant potential difference decreases current because charge flow is opposed more strongly.

IB Command-Term Frames for Circuits

Use different answer shapes for different command terms:

• State: give the equation, definition, or named quantity directly.
• Calculate: show substitution and unit, then round sensibly.
• Explain: describe the relationship and the physical reason.
• Compare: say what is the same and what is different between two circuits or components.

This is where many IB answers lose marks. A correct calculation does not automatically answer an explanation prompt.

Concept Check Before Question Practice

Before doing a timed set, answer these in words:

1. What does a voltmeter measure in terms of energy and charge?
2. Why does current decrease if resistance increases at constant voltage?
3. What does higher power mean for energy transfer per second?

If those answers are clear, the equations become easier to use under pressure.

IB Physics Circuits: Explain Energy and Charge Clearly

For IB Physics, electric circuits questions often reward conceptual wording as much as calculation. Before using an equation, make sure you can explain what the quantities mean:

• Current is how much charge passes a point per second.
• Potential difference is energy transferred per unit charge.
• Resistance describes how strongly a component opposes current.
• Power is the rate at which energy is transferred.
• A circuit explanation should mention charge flow or energy transfer, not only a memorised formula.

When a command term says explain, do not stop at V = IR. Say what changes, why it changes, and what stays constant. For example, if resistance increases at constant potential difference, current decreases because the same energy-per-charge is driving charge through a larger opposition.

What Makes This Topic Different

Electric circuits combine definitions with diagnosis. A formula answer may calculate the right number, but explanation questions often ask why current changes, why a component gets dimmer, or why resistance affects power.

Use two columns when practising: left column for calculation, right column for physical explanation. This trains you to move between equations and circuit behaviour instead of treating them as separate topics.

Worked Examples

Worked Example 1: Current in a Series Circuit

Question: Two lamps are connected in series. What happens to current through each lamp?

Worked answer: The current is the same through each component in a series circuit because there is only one path for charge to flow. The potential difference is shared, but current is not split.

Markscheme-style answer:

• Series circuit has one path.
• Current is the same through each component.
• Potential difference may be shared between components.

Worked Example 2: Resistance from I-V Data

Question: A component has potential difference 4.0 V and current 0.20 A. Find resistance.

Worked answer: Use R = V / I. Resistance = 4.0 / 0.20 = 20 ohms. The unit matters because resistance is measured in ohms.

Markscheme-style answer:

• Selects R = V / I.
• Substitutes values correctly.
• Calculates 20 ohms.
• Includes correct unit.

Editorial Review

This guide was prepared by the EduNinja Editorial Team and reviewed for syllabus alignment, study usefulness, and answer quality. It is designed as independent revision support and should be checked against your current school or exam-board specification when a course has changed.

Start From the Matching EduNinja Notes

This article is meant to sit next to the EduNinja Notes page, not replace it. Start with the most relevant note, then come back here for the worked examples and markscheme-style answer checks.

• IB Physics Notes

A good study loop is:

1. Open IB Physics Notes and rebuild the key definition, diagram, or method.
2. Return to this article and try the worked examples without looking.
3. Mark your answer for exact wording, units, and missing steps.
4. Move from notes into question practice only after the concept is clear.

FAQ

How should I revise Electric Circuits for IB Physics?

Start with a short note review, then answer exam-style questions as quickly as possible. The topic only becomes secure when you can retrieve the idea without notes and apply it to unfamiliar wording.

Are notes enough for this topic?

Notes are enough to learn the structure, but not enough to check exam readiness. Use notes to rebuild the concept, then use question practice to test whether your answer includes the exact wording, units, sequence, or explanation the markscheme rewards.

What should I do if I keep making the same mistake?

Write the mistake as a specific correction, not a general complaint. For example, "I confuse strong and concentrated" or "I forget the constant of integration." Then practise one targeted question and make a flashcard from the correction.

Which EduNinja link should I open first?

Open the notes or topic page that matches your weakest subtopic first. If you are not sure, start from the subject question bank and choose a small question set rather than trying to revise the whole chapter.

Related Articles and Study Links

• IB Physics Question Bank
• B.5.13 Series and parallel circuits
• IB Physics Notes
• B.5 Current and circuits
• A.1.9 Fluid resistance on projectiles