Ohm’s Law is one of the most important relationships in IB Physics, forming the foundation of your understanding of electric circuits. Whether you're analyzing series and parallel components, interpreting I–V graphs, or designing your Internal Assessment, this law helps you predict how electrical quantities interact. Students aiming for top grades benefit from mastering Ohm’s Law early since it appears across all exam papers. This focus on fundamentals is reflected in The Quest for a 7 in IB Physics (https://www.revisiondojo.com/blog/the-quest-for-a-7-in-ib-physics) , which identifies electrical basics as high-value exam content.
What Ohm’s Law States
Ohm’s Law states that:
The current through a conductor is directly proportional to the voltage across it, provided the temperature remains constant.
In formula form:
V = IR
Where:
- V = potential difference (volts, V)
- I = current (amperes, A)
- R = resistance (ohms, Ω)
This simple equation allows you to calculate any of the three quantities as long as the other two are known. It also becomes the foundation of nearly every electricity topic in the IB Physics syllabus.
Students who review the official Data Booklet regularly—assisted by resources like the IB Physics Formula Sheet & Data Booklet Guide (https://www.revisiondojo.com/blog/ib-physics-formula-sheet-data-booklet-ultimate-2025-guide-must-know-tips) —tend to recall and apply this formula far more confidently in exams.
The Conditions for Ohm’s Law
Ohm’s Law only applies if the temperature is constant.
When temperature changes, resistance may change, meaning the relationship between V and I no longer remains proportional.
This is why:
- Filament lamps do not obey Ohm’s Law
- Thermistors and diodes do not follow a straight-line V–I relationship
- Metals with rising temperature show increased resistance
Understanding these exceptions is important for interpreting real circuit behavior and for answering qualitative questions on Paper 2.
I–V Graph Interpretation
A key part of IB Physics is analyzing I–V graphs:
- Ohmic conductor: straight line through the origin (constant resistance)
- Non-ohmic conductor: curve showing changing resistance
- Diode: current flows only after a threshold voltage
Being able to read these graphs quickly is essential for exam speed and accuracy. Students preparing for high performance often practice these graph interpretations using structured strategies from How to Get a 7 in IB Physics (New Syllabus 2025 Onward) (https://www.revisiondojo.com/blog/how-to-get-a-7-in-ib-physics-new-syllabus-2025-onward) .
Applying Ohm’s Law in IB Physics
Ohm’s Law is useful for:
- Calculating voltage, current, or resistance
- Designing circuits with desired current values
- Selecting resistors for protection
- Determining power (P = IV, P = I²R, P = V²/R)
- Analyzing series and parallel circuits
- Understanding internal resistance of power supplies
These calculations appear in both Paper 1 and Paper 2, making Ohm’s Law a high-frequency exam topic. The consistency of its appearance helps explain why electrical topics strongly affect exam performance, something reinforced in IB Physics Grade Boundaries Explained (https://www.revisiondojo.com/blog/ib-physics-grade-boundaries-explained-what-you-need-to-know-for-success) .
Ohm’s Law in the Internal Assessment
Many excellent IAs are based on Ohm’s Law or variations of it. Common investigations include:
- I–V characteristics of different materials
- How wire length affects resistance
- How temperature affects resistance
- How cross-sectional area affects current
- Determining internal resistance of a power source
For more ideas based on resistive behavior and circuit design, students often explore Top 10 Fresh IB Physics IA Ideas 2025 (https://www.revisiondojo.com/blog/top-10-fresh-ib-physics-ia-ideas-2025-how-revisiondojo-can-supercharge-your-ia) .
Common Misconceptions
Students often believe that:
- All components obey Ohm’s Law (many do not)
- Resistance stays constant even when temperature changes
- A straight-line graph is always required for Ohm’s Law (only ohmic materials obey it)
- Voltage causes current in a simplistic sense (the relationship is more nuanced)
Clearing up these ideas early makes electricity far easier to manage throughout the course.
For rapid revision of core electricity concepts, many students use compressed strategies from How to Cram IB Physics in 1 Week (https://www.revisiondojo.com/blog/how-to-cram-ib-physics-new-syllabus-2025-onward-in-1-week-a-survival-guide) .
FAQ
Does Ohm’s Law apply to all conductors?
No. Only materials with constant resistance obey the law.
Why does temperature matter?
Because increasing temperature increases particle collisions, changing resistance.
Is the resistance always constant in a resistor?
For an ohmic resistor, yes. For non-ohmic components, no.
RevisionDojo Call to Action
If you want to master circuits, formulas, and the entire electricity unit, RevisionDojo gives you the structured explanations and exam strategies needed for success. Whether for exams or your IA, RevisionDojo supports your learning every step of the way.
