Photoelectric Effect Simulator

Free photoelectric effect simulator: change the metal, wavelength, intensity and voltage and watch electrons leave the surface. See the threshold frequency, stopping voltage, kinetic energy and current graphs, and measure Planck's constant from your own data.

Metal surface

Wavelength:

Intensity: More intensity = more photons per second, not more energy per photon.

Collector voltage: Positive pulls electrons in, negative pushes them back.

Try

Photon energy

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Max kinetic energy of electrons

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Stopping voltage

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Threshold of this metal

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Photocurrent now

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Current against voltage

The current stops at the stopping voltage −V₀, however bright the light. Brighter light only makes the whole curve taller. (Idealised curve.)

Electron energy against frequency

A straight line whose slope is Planck's constant h and whose intercept is −φ. Nothing is emitted left of the threshold, even with very bright light.

Measure Planck's constant yourself

Choose a metal, then for several wavelengths find the stopping voltage (or just press Record) and add the point. Four or five different colours are enough for the fit to find h and the work function.

Add realistic measurement noise (±0.03 V)

Wavelength (nm)	Frequency (10¹⁴ Hz)	Stopping voltage (V)

Record at least two points above the threshold.

The photoelectric effect

When light shines on a metal, electrons can be knocked out of its surface. In 1905 Einstein explained the puzzling details by treating light as a stream of packets of energy called photons, each carrying energy E = h f, where f is the frequency and h is Planck's constant. An electron leaves only if one photon gives it at least the metal's work function φ, the energy needed to escape. Any energy left over becomes kinetic energy:

KE_max = h f − φ V_stop = KE_max / e f₀ = φ / h

What this simulator shows

Move the wavelength slider and watch electrons switch on and off at the threshold. Red light never works on caesium, however intense; blue light does immediately.
Change the intensity: more photons arrive, so more electrons come out and the current rises, but their top energy does not change.
Change the collector voltage to push electrons back. When the voltage reaches the stopping voltage the current falls to zero: that measures the electrons' maximum energy.
Measure h: record the stopping voltage at several frequencies and the table fits a straight line. Its slope times e gives Planck's constant (6.626 × 10⁻³⁴ J·s) and its intercept gives the work function.

Why it mattered

Observation	Wave theory predicted	What happens (photons)
Brighter light	electrons come out faster	more electrons, same top speed
Light of low frequency, very bright	should eventually work	never works below the threshold frequency
Dim light of high frequency	a delay while energy builds up	electrons appear instantly
Higher frequency	no effect on energy	top energy rises linearly with f

Einstein received the 1921 Nobel Prize for this explanation, a founding step of quantum mechanics. The same effect powers solar cells, light meters, night-vision tubes and photomultipliers.

Notes on accuracy

Energies, wavelengths and stopping voltages follow the exact formulas with CODATA constants. Work functions are typical textbook values; real ones vary by about a tenth of an electronvolt with surface cleanliness and crystal face. The current curve is an idealised shape, and the animation is a qualitative picture: electron speeds are drawn slowly and photon counts are scaled for visibility.

Related: Unit Conversion · Calculator · More MES tools

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