When most people think of the International Physics Olympiad (IPhO), they picture students hunched over exam papers, wrestling with complex theoretical problems in a silent hall. And indeed, the five-hour theoretical examination is a formidable challenge. But there is another half of the competition — one that receives far less attention but is, in many ways, the truest test of a physicist's ability. This is the experimental examination: five hours in the laboratory, where students must design, execute, and analyse a sophisticated physics experiment with nothing but their wits, a bench of equipment, and a problem statement. In this article, we pull back the curtain on the IPhO experimental exam, exploring what it involves, why it matters, and how aspiring olympians can develop the hands-on skills needed to excel.
What Is the Experimental Exam?
At every International Physics Olympiad, students face two separate examinations, each lasting five hours:
The Theoretical Examination: three long-form problems covering the breadth of pre-university physics, solved on paper
The Experimental Examination: one or two laboratory-based problems, solved at a workbench with real equipment
The experimental exam is unique among academic olympiads. The International Mathematical Olympiad, the Chemistry Olympiad (which has an experimental component but of a very different character), and the Biology Olympiad all test primarily written or analytical skills. Only the IPhO demands that students demonstrate genuine laboratory competence — the ability to set up apparatus, align optical components, calibrate instruments, collect data systematically, identify and quantify errors, and present their findings in a clear scientific report.
What Kinds of Experiments Are Set?
The experimental problems at the IPhO are carefully designed to test a wide range of practical skills. They are drawn from all areas of physics and typically involve at least some of the following:
Optical Experiments
Measuring the refractive index of a transparent material using laser interferometry or prism deflection
Determining the wavelength of a laser using diffraction gratings or double-slit arrangements
Characterising the properties of a lens system, including focal length, aberrations, and resolution limits
Investigating polarisation phenomena and verifying Malus's law
Electrical and Electronic Experiments
Characterising the behaviour of capacitors, inductors, and non-standard circuit components
Measuring the speed of electromagnetic signals in cables using pulse techniques
Using oscilloscopes to analyse AC circuits, transient responses, and filter characteristics
Investigating semiconductor devices such as diodes, transistors, or thermistors
Mechanical Experiments
Measuring the acceleration due to gravity using pendulums, free-fall apparatus, or oscillating systems
Investigating the moment of inertia of irregular objects
Determining the speed of sound in air using resonance tubes or time-of-flight measurements
Studying damped and driven harmonic oscillators
Thermal Experiments
Measuring the specific heat capacity of a material using electrical heating methods
Investigating the Stefan-Boltzmann law by measuring thermal radiation from a filament
Studying heat transfer mechanisms (conduction, convection, and radiation) in controlled setups
What Skills Are Really Being Tested?
Beyond the specific physics content, the experimental exam is fundamentally a test of scientific thinking under real-world constraints. Here are the key competencies that distinguish the top performers:
1. Experimental Design and Strategy
Students are typically given a problem statement rather than a step-by-step procedure. The first and most crucial skill is deciding how to approach the problem. Which measurements should be taken first? Which quantities can be determined directly and which must be derived? How can systematic errors be minimised? How should the available time be allocated between setup, data collection, analysis, and write-up?
Top performers develop a systematic approach to experimental design, often drawing on experience from training camps and previous competitions. They know, for example, that it is usually wise to start with a quick sanity-check measurement before committing to a detailed procedure, and that leaving adequate time for write-up (at least 60–90 minutes) is essential.
2. Manual Dexterity and Instrument Handling
The experimental exam is, at its heart, a practical test. Students must manipulate real equipment — aligning laser beams to sub-millimetre precision, soldering circuits, adjusting micrometers, reading scales through magnifying glasses, and handling delicate optical components without contamination. These are skills that cannot be developed by reading textbooks — they require hours of hands-on practice in the laboratory.
3. Error Analysis and Uncertainty
This is perhaps the single most important skill for the experimental exam — and the one where most students lose the most marks. Every measurement carries uncertainty, and a top-quality experimental report must:
Identify the sources of uncertainty in every measurement (instrumental precision, reading errors, environmental fluctuations, systematic effects)
Quantify these uncertainties using appropriate statistical methods (standard deviations, propagation of errors, confidence intervals)
Distinguish between statistical uncertainties (which can be reduced by taking more data) and systematic uncertainties (which cannot)
Present results with the correct number of significant figures and appropriate units
Use graphical methods (error bars, best-fit lines, residual analysis) to extract relationships from data
4. Scientific Writing and Communication
At the end of five hours, students must hand in a written report that clearly communicates what they did, what they found, and how confident they are in their results. The report must include:
A clear statement of the methodology used
Well-organised tables and graphs of raw and processed data
A logical analysis that connects the measurements to the physics
An honest and thorough error analysis
Clear conclusions with stated uncertainties
The ability to communicate complex experimental work clearly and concisely is a skill that separates the good from the great. Many students with strong technical abilities lose marks simply because their write-up is disorganised, incomplete, or unclear.
Why the Experimental Exam Matters
The experimental exam is not just a quirky feature of the IPhO — it is a fundamental statement about what it means to be a physicist. Physics is, at its heart, an experimental science. Theories are built on observations, tested against measurements, and ultimately validated or refuted by experiments. A physicist who can solve beautiful equations but cannot design an experiment to test them is, in a profound sense, incomplete.
The IPhO experimental exam also serves a practical purpose for national selection. Students who excel at both theoretical and experimental physics are rare and valuable — they are the ones who go on to make genuine contributions to the field. By testing experimental skills explicitly, the IPhO ensures that the medals recognise complete physicists, not just brilliant calculators.
For the BPhO and the UK team, the experimental exam is particularly significant. At IPhO 2024 in Isfahan, the UK's Ewan McMillan won the prestigious Experimental Prize — awarded to the student with the highest experimental score worldwide — a testament to the strength of the UK's emphasis on practical physics skills.
How to Prepare for the Experimental Exam
For students aspiring to reach the IPhO — and particularly for those hoping to be selected for the UK team — developing experimental skills is essential. Here is a comprehensive guide to preparation:
Start in Your School Laboratory
The best preparation begins with the equipment you have access to. Even simple experiments — measuring g with a pendulum, verifying Snell's law with a glass block, determining the speed of sound with a resonance tube — build the fundamental skills of experimental physics. The key is not the sophistication of the equipment but the rigour of the approach:
Take multiple readings and calculate means and standard deviations
Identify systematic errors (zero errors, parallax, friction) and estimate their effects
Draw graphs with error bars and determine relationships using line-of-best-fit techniques
Write up every experiment as if it were a formal lab report — even if your teacher does not require it
Learn to Use Standard Laboratory Equipment
Familiarise yourself with the equipment commonly used in olympiad experiments:
Oscilloscopes: Learn to read time-base and voltage settings, trigger signals, measure phase differences, and analyse Lissajous figures
Multimeters: Practice measuring resistance, voltage, and current accurately, and understand the limitations of each measurement mode
Optical equipment: Gain experience with lasers, diffraction gratings, lenses, mirrors, polarisers, and beam splitters
Mechanical apparatus: Work with calipers, micrometers, stopwatches, photogates, and force sensors
Signal generators and function generators: Learn to produce sine, square, and triangular waves, and understand frequency, amplitude, and impedance
Practice Under Timed Conditions
The five-hour time limit is one of the most challenging aspects of the experimental exam. In training, set up full-length practice experiments and work under strict time pressure. Force yourself to:
Plan your approach before touching any equipment (15–20 minutes)
Set up and verify your apparatus (30–45 minutes)
Collect data systematically (90–120 minutes)
Analyse data and calculate results (45–60 minutes)
Write up your report (60–90 minutes)
Study Real Experimental Papers
Reading published experimental physics papers — even at an undergraduate level — is an excellent way to understand how professional physicists design experiments, analyse data, and communicate results. Pay attention to:
How the authors describe their experimental setup
How they quantify uncertainties and justify their error analysis
How they use graphs and tables to present data
How they discuss limitations and suggest improvements
Attend Training Camps and Workshops
For students selected for the BPhO training camp at Oxford, the experimental training is intensive and world-class. Even for those not yet at camp level, many universities and physics societies offer experimental workshops and summer schools. Seek these out — they provide access to equipment and expertise that simply is not available in most school laboratories.
The UK's Strength: Why British Students Excel at Experimental Physics
The UK has a particularly strong tradition of experimental physics, and this is reflected in the performance of UK students at the IPhO experimental exam. Several factors contribute to this strength:
A-level practical requirements: The UK A-level physics curriculum includes mandatory practical components, ensuring that all students gain some laboratory experience
BPhO emphasis: The BPhO training camp includes substantial experimental sessions, preparing students for the IPhO exam
University laboratory culture: The UK's ancient universities have a deep tradition of hands-on experimental physics, and this culture permeates the training programme
Isaac Physics and practical resources: Online platforms and teacher training initiatives are increasingly incorporating experimental skills alongside theoretical problem-solving
The result is that UK students often approach the experimental exam with a level of confidence and competence that surprises students from countries with stronger theoretical traditions. This is a genuine competitive advantage — and one that the BPhO programme works hard to maintain.
Looking Ahead: The Future of Experimental Physics at the IPhO
As experimental physics in the real world becomes increasingly sophisticated — with gravitational wave detection, quantum computing, and nanotechnology pushing the boundaries of what can be measured — the IPhO experimental exam will continue to evolve. We can expect:
More experiments involving digital data acquisition and computer-based analysis
Greater emphasis on interdisciplinary experiments that combine physics with engineering, materials science, or biology
Increased use of modern sensors and instruments that would have been unimaginable a generation ago
Continued focus on error analysis and uncertainty quantification as the intellectual core of experimental physics
For students preparing for the experimental exam, the message is clear: the fundamentals — careful measurement, rigorous analysis, clear communication — will never go out of style. Master these, and you will be prepared for whatever the IPhO throws at you, whether it involves a 19th-century prism or a 21st-century quantum sensor.
Final Thoughts: The Joy of Experimental Physics
For all its challenges, the experimental exam is also one of the great joys of the IPhO experience. There is something profoundly satisfying about setting up an apparatus, watching the data emerge, and realising that you are measuring something real — the speed of light, the charge of an electron, the curvature of spacetime — with your own hands and your own mind. It is physics made tangible, and for many students, it is the moment when their love of the subject becomes truly deep and lasting.
If you are a student with access to a laboratory — even a modest school lab — seize the opportunity. Spend time with the equipment. Run experiments that interest you. Learn to trust your instruments and to question your results. The skills you develop will serve you well not just at the IPhO, but throughout your life as a scientist, an engineer, or simply a person who understands the world a little more clearly.
For more information about experimental physics preparation, visit the British Physics Olympiad or explore the resources at Isaac Physics.
