Physics IA · E · Nuclear and quantum physics · topic 27 of 30
Photoelectric effect: stopping voltage vs frequency · IB Physics IA idea: guide, sample graph and step-by-step plan
a classic. make the simulation part honestEinstein said light comes in packets. Your graph is a straight-line test of that, if you do it carefully.
- ✓ you like a theory you can test
- ✓ you can make a clean straight-line graph
- ✓ you are careful about what a simulation is
The big idea
← 'model, not experiment'Einstein's equation eV_s = hf − φ predicts a straight line of stopping voltage against frequency. Its gradient is h/e and its intercept gives the work function. Below a threshold frequency, no electrons escape at all. A simulation gives you exact, quick data, but it is a model, not an experiment: you must say so, and ask what it can and cannot show. Where does the 'noise' in your data come from? In a simulation, it is your reading and the slider steps.
Make it yours: pick one twist
Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.
Swipe for more twists →
Repeat for two or three metals in the simulation.
→ Lines with the same gradient but different intercepts: a strong test of the theory, and you can rank work functions.Keep the frequency fixed and change the intensity, then check what happens to the stopping voltage and to the current.
→ A test of the photon model: intensity should not change the stopping voltage. A clean prediction to confirm or break.Use the gradient to find a value of Planck's constant and compare it with the accepted one.
→ A number with an uncertainty and a percentage difference: a convincing conclusion.Decide what a classical wave model predicts and compare it with the simulation.
→ Your evaluation is about two models, not just one.Use LEDs of different colours and their turn-on voltages for a rough real-data estimate of h/e, and compare it with the simulation.
→ A second, quite different data set: you can discuss how far a simulation and an experiment agree, and why not exactly.Solar cells, light sensors or night-vision tubes.
→ Gives your introduction a purpose; the physics and the graph stay the same.Your Physics IA research question: run the check
say which simulationWrite your own question first. Then make sure it ticks every box:
- Names the independent variable (frequency, or wavelength converted to frequency) and its range, with several values.
- Names the dependent variable and how the simulation lets you find it (the voltage at which the current just reaches zero).
- Says what stays fixed: the metal, the intensity and the simulation settings.
- Says what you will find or compare: the work function, h, or a threshold frequency.
- Says plainly that the data is from a simulation, and which one.
The set-up
What the simulation shows, redrawn as a sketch. Name your simulation, its version and the settings you chose.
How your Physics IA could be laid out
The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.
Your question; where the photoelectric effect matters (solar cells, sensors) and why it changed physics; what you expect.
Photons and the equation eV_s = hf − φ; threshold frequency; what the gradient and intercept mean; what the wave model would predict instead.
Independent, dependent and controlled variables, with how the simulation sets or reads each.
Name and version of the simulation, settings, how you find the stopping voltage (what 'just zero' means), step sizes, repeats, and how you convert wavelength to frequency.
Short: screen time and nothing else. You may also note that no apparatus was used.
One table with frequency or wavelength, stopping voltage, and uncertainties from the slider steps and your reading.
How you get frequency and its uncertainty, how you find the voltage and its uncertainty; one worked example of each.
A graph of stopping voltage against frequency, error bars, a best-fit line, and what gradient and intercept mean. Include points below threshold.
Answer with numbers: h or the work function with uncertainty, compared with the accepted value; what the simulation can and cannot tell you.
Weaknesses ranked by their effect on your result, each with a specific, realistic improvement.
Every source for theory, method, data or simulation.
What your Physics IA graph could look like
explain where the error bars come fromMade-up data, to show you the form of a strong graph, not the answer. Yours will look different. example only
- Axis labels say the quantity, the unit and the uncertainty. The 10¹⁴ in the label means the numbers on the axis are small.
- Error bars come from the slider step and how well you can tell the current is zero: a simulation has no random noise, so say where the spread comes from.
- A second metal drawn to show the same gradient with a different intercept.
- Points are close to the line because a simulation is exact; do not overclaim agreement. The question is what the line can tell you about the model.
- Another graph to consider: plot V_s against f for several intensities. The lines should lie on top of each other if the photon model holds.
Which reading limits your value of h?
Rank by the effect on your result, the gradient h/e from the line, not on each reading. The voltage reading is likely to matter most, and that points to a fix.
Your game plan
Tick steps off as you go. We'll remember on this device.
0 of 11 done
- Read and predictFind the photoelectric equation, the idea of a threshold and the work function. Predict the graph, and say what a wave model would predict instead.
- Choose and describe the simulationPick one, note its name and version, and decide what you can set and read. A simulation is a model: say what it assumes and who made it.
- Trial run (1 lesson)Explore: does the intensity change the stopping voltage? What is the smallest step on the sliders? How do you decide the current is zero?
- Choose range and valuesChoose at least 6 frequencies across the metal's range, including some near the threshold and some below it.
- Collect the dataRecord wavelength or frequency and stopping voltage in a table. Repeat a few settings to see how well you can reproduce a reading.
- ProcessConvert to frequency, give uncertainties for both axes, and decide how you will find the gradient and intercept.
- Graph and fitPlot V_s against f with error bars, find the line and its uncertainty, and say what each part means.
- Compare with theoryCompare h and the work function with accepted values, in terms of your uncertainties and a percentage difference.
- EvaluateRank the limits on your result, and be specific about what the simulation cannot show you.
- Write, then cutWrite in the order of the layout above and keep within 3,000 words: tables, graphs, equations and references are not counted, so let them carry detail.
- Check before your teacher's draftRun the checklist below, then get your RQ or draft checked. Your teacher reads one draft only, so make it count.
Physics you'll need
Traps to avoid in this Physics IA
examiners look for this one!- Treating simulation output as real data without saying it is a model.
- Too few frequencies, or none near or below the threshold.
- Mixing wavelength and frequency, or forgetting the factor of 10¹⁴ in the gradient.
- Claiming 'no uncertainty' because the simulation is exact: your reading and the slider steps still limit it.
- Forcing the line through the origin when the intercept is the work function.
- Not saying what the wave model would have predicted, so the result tests nothing.
More Physics IA ideas like this
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- Counting radiation: does it follow an inverse square?●●●
- Shielding radiation: the absorption coefficient●●●
This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.