IB DP Physics skill pack: uncertainties on a graph, SL and HL (first assessment 2025). Uncertainty bars, extreme lines, gradient and intercept uncertainty, and linearizing: the four moves a Paper 1B analysis is marked on.

What this pack is, and what it is not
The IB guide asks for these techniques to be practised inside the topics and the investigations that need them, so this is not a taught unit of the course and does not claim to be one. It is reference and remedial material for a technique the whole of practical physics assumes: it supplements integrated teaching rather than replacing it. It earns its place once a class has met uncertainties in arithmetic and is about to meet them on a graph for the first time, again as revision before the internal assessment and before Paper 1B, and any time a student is losing marks on the construction rather than on the physics.
This pack is worked, not taught: the 200 minutes quoted is student working time across the practice bank, not classroom delivery time. Set it as homework and practice rather than as a timed classroom activity. It runs as five sittings of about 31, 32, 39, 44 and 50 minutes, and the worksheet says on the page where each break falls. Ruler work is slower than it looks, and every construction here is a full one: the drawing is the technique itself and not a tidy way of writing it up, which is why the applied sitting is longer than its three questions suggest.

Where this pack starts
It assumes the arithmetic of uncertainty rather than teaching it. The rules at the head of the pack restate exactly as much of it as the graph work needs, absolute against fractional and percentage uncertainty, the rule for a sum or a difference, the rule for a product or a quotient, the power rule and the exact-number rule, so the pack can be worked with nothing else to hand. A class that has never propagated an uncertainty should meet that first. What this pack owns is what uncertainty does to a graph once the readings are in front of you.

What students learn

• The uncertainty that becomes a bar.
• The line of best fit, and the two extreme lines.
• A gradient, an intercept, and the uncertainty in each.
• Linearizing, and only where it is appropriate.
• The intercept read as a diagnostic.

IB skills this pack teaches and practises

• Drawing and interpreting uncertainty bars (taught).
• Constructing lines of maximum and minimum gradient by eye, considering all the uncertainty bars (taught). T
• Determining the uncertainty in gradients and intercepts (taught).
• Linearizing graphs, only where appropriate (taught).
• Drawing lines of best fit (practised).
• Plotting graphs with appropriate scales and axes (practised).
• Propagating uncertainties in processed data (practised).
• Identifying and discussing sources and impacts of random and systematic errors (practised).

What’s in the pack

• Student Worksheet (31 pages)
• Teacher Key (45 pages)
• The editable worksheet**