IB Physics Paper 1B: Data-Based Questions and Technique

IB Physics Paper 1B is the data-based section of Paper 1 in the syllabus first examined in May 2025. It carries 20 marks at both SL and HL, it is sat in the same session as the multiple-choice Paper 1A, and it asks you to analyse experimental data: tables, graphs, uncertainties and conclusions.

Where it sits in the exam.

Paper 1 lasts 1 hour 30 minutes at SL (25 multiple-choice marks plus 20 marks of Paper 1B) and 2 hours at HL (40 multiple-choice marks plus 20 marks of Paper 1B). Together, Paper 1 is worth 36% of the final grade, with Paper 2 at 44% and the internal assessment at 20%. The data booklet and a calculator are allowed.

Why it replaced Paper 3.

The old syllabus had a Paper 3 whose Section A tested data analysis and whose Section B tested options. The options have gone, and so has Paper 3. The experimental skills it examined now sit inside Paper 1B, which means every candidate, SL or HL, meets uncertainties and graph work in the first paper they sit.

The timing that follows from the marks.

Both versions of Paper 1 give you almost exactly two minutes per mark, so Paper 1B deserves about 40 minutes. Many students leave it to the end and rush it. My advice is the opposite: Paper 1B rewards steady written method, while the multiple choice rewards speed, so do 1B while your attention is fresh.

This article is organised around the mistakes I see most often when my students work through Paper 1B under timed conditions, each one paired with the habit that fixes it. If you are still deciding your level, my comparison of IB Physics HL and SL explains what changes between the two papers.

In IB Physics Paper 1B you read a data table by checking three things first: the quantity and unit in each column heading, the stated uncertainty, and the number of decimal places. A value and its uncertainty must agree in decimal places, and a raw uncertainty is normally quoted to one significant figure.

Mistake 1: inconsistent significant figures.

Writing $2.346 \pm 0.1\,\text{m}$ tells the examiner you do not understand what the uncertainty means. The uncertainty fixes the last meaningful digit, so the correct form is $2.3 \pm 0.1\,\text{m}$. In processed data, a calculated value should carry no more significant figures than the least precise measurement that produced it.

Mistake 2: missing or wrong error bars.

When a question asks you to plot points, draw an error bar whenever the uncertainty is larger than the dot itself. An error bar is the full range from value minus uncertainty to value plus uncertainty, so a point at $y = 4.0$ with $\Delta y = 0.3$ needs a bar from 3.7 to 4.3, not from 4.0 to 4.3.

Mistake 3: a line that joins the dots.

A line of best fit is a single straight line or smooth curve with points scattered on both sides. It does not have to pass through the origin, and it should pass through the error bars where it can. If one point sits far from the rest, say so: identifying an anomalous point is often a mark in its own right.

Mistake 4: forgetting units on processed axes.

If you plot $T^2$ against $m$, the vertical axis is in $\text{s}^2$, and the gradient is in $\text{s}^2\,\text{kg}^{-1}$. Units on a gradient or intercept are routinely required by the markscheme, and a correct number with no unit can lose the final mark.

IB Physics uses three propagation rules, all printed in the data booklet. When quantities are added or subtracted, add their absolute uncertainties. When they are multiplied or divided, add their fractional uncertainties. When a quantity is raised to a power $n$, multiply its fractional uncertainty by $|n|$.

In symbols, for $y = a \pm b$ the rule is $\Delta y = \Delta a + \Delta b$, and for $y = \frac{a^n b^m}{c}$ it is:

$$\frac{\Delta y}{y} = |n|\frac{\Delta a}{a} + |m|\frac{\Delta b}{b} + \frac{\Delta c}{c}$$$$\begin{aligned}\frac{\Delta y}{y} &= |n|\frac{\Delta a}{a} + |m|\frac{\Delta b}{b} \\ &\quad + \frac{\Delta c}{c}\end{aligned}$$

Mistake 5: adding absolute uncertainties in a product.

If a resistance comes from $R = \frac{V}{I}$, you cannot add $\Delta V$ in volts to $\Delta I$ in amperes: the units alone tell you it is meaningless. Convert each to a fractional or percentage uncertainty first, add those, then convert back by multiplying by $R$.

Mistake 6: forgetting the power.

A period of $T = 0.80 \pm 0.02\,\text{s}$ has a fractional uncertainty of $\frac{0.02}{0.80} = 0.025$. For $T^2 = 0.64\,\text{s}^2$ the fractional uncertainty doubles to $0.05$, so $\Delta(T^2) = 0.05 \times 0.64 \approx 0.03\,\text{s}^2$ and the result is $T^2 = 0.64 \pm 0.03\,\text{s}^2$. Students who skip the factor of 2 lose the mark even with perfect arithmetic.

Mistake 7: subtracting uncertainties.

In a difference such as $\Delta\theta = \theta_2 - \theta_1$, the uncertainties still add. A difference of two close values can therefore have a very large percentage uncertainty, and a good 'suggest' answer often points exactly at that weakness in the method.

These are the same rules you apply in your own investigation, so the uncertainty section of my IB Physics internal assessment guide is useful practice for Paper 1B too.

In IB Physics Paper 1B, 'estimate' asks for an approximate value from the data or the graph, 'suggest' asks for a plausible idea applied to this specific experiment, and 'outline' asks for a brief account in a sentence or two. The command word sets the depth of answer the markscheme expects.

Mistake 8: answering 'suggest' with a textbook definition.

'Suggest' signals that the context is new and that more than one answer can earn the mark. 'Suggest one improvement to the experiment' is never answered by 'repeat the readings' alone. The markscheme wants an improvement tied to the specific weakness: 'use a light gate to time the oscillation, because the reaction time is large compared with $T$'.

Mistake 9: over-precise estimates.

'Estimate' means a value read or calculated roughly, often from a graph, quoted to a sensible number of significant figures. Giving four significant figures for a value read off a hand-drawn line contradicts the command word. One or two significant figures, with a unit, is usually right.

Mistake 10: writing a paragraph for 'outline' or 'state'.

For 'state' one word or phrase earns the mark, and 'outline' needs a short account, not an essay. Extra sentences cost you time and can introduce a wrong statement that cancels a correct one. Match the length of your answer to the number of marks shown.

The table below lists the command words that come up most often in Paper 1B and what each one demands.

To find a gradient with its uncertainty in IB Physics, draw the line of best fit and two extra lines: the steepest and the shallowest that still pass through every error bar. The best-fit gradient is the value, and half the difference between the steepest and shallowest gradients is its absolute uncertainty.

The question.

A student hangs masses $m$ on a spring and times the period $T$. Theory gives $T = 2\pi\sqrt{\frac{m}{k}}$, so squaring:

$$T^2 = \frac{4\pi^2}{k}\,m$$

A graph of $T^2$ against $m$ is a straight line through the origin with gradient $\frac{4\pi^2}{k}$. You are asked to determine $k$ with its uncertainty.

Step 1: the best-fit gradient.

Use a large triangle on the line, not two data points. Suppose the line gives $0.160\,\text{s}^2\,\text{kg}^{-1}$. Reading coordinates from the line, across at least half of the plotted range, is what the markscheme rewards.

Step 2: the extreme lines.

Through the error bars of the first and last points, draw the steepest and shallowest lines. Suppose they give $0.172$ and $0.150\,\text{s}^2\,\text{kg}^{-1}$. The uncertainty is $\frac{0.172 - 0.150}{2} = 0.011$, so the gradient is $0.16 \pm 0.01\,\text{s}^2\,\text{kg}^{-1}$.

Step 3: the physical quantity.

From the gradient, $k = \frac{4\pi^2}{0.160} \approx 247\,\text{N}\,\text{m}^{-1}$. The fractional uncertainty carries over unchanged: $\frac{0.011}{0.160} \approx 0.07$, so $\Delta k \approx 0.07 \times 247 \approx 17$. Rounded to one significant figure, $k = 250 \pm 20\,\text{N}\,\text{m}^{-1}$.

Mistake 11: one line, no uncertainty.

Students who draw only the best-fit line, or who take the extreme lines through two random points rather than the error bars, lose the uncertainty marks. A second classic slip is to quote $k = 246.7 \pm 17$: the value must stop at the same decimal place as the rounded uncertainty.

Mistake 12: ignoring the intercept.

If the best-fit line misses the origin by more than the error bars allow, Paper 1B often asks why. 'Suggest' answers such as 'the mass of the spring itself was not included in $m$' identify a systematic error, which is exactly the physics being tested.

A student who is ready for IB Physics Paper 1B can take a past data question, draw a graph with error bars and a gradient uncertainty in about 40 minutes, and explain each step aloud. If your child only revises formulas and multiple choice, the data section is probably under-prepared.

Questions you can ask without knowing physics.

Ask your child to show you a graph they drew in a recent practice paper and to point at the error bars and the two extra lines. Ask how many marks Paper 1B is worth and how long they plan to spend on it. Clear, quick answers are a good sign.

How to support them.

Paper 1B practice needs a printed paper, graph paper, a ruler and a quiet, timed slot, so help protect that time. Past papers from May 2025 onwards follow the new format; my guide to finding IB past papers explains where to get them, and older Paper 3 Section A questions remain useful practice.

If the exams are close, the six-week revision plan for IB Maths and Physics shows how to fit data practice into the final weeks without crowding out everything else.