Modern Physics · Physics

Photoelectric Effect Simulation

Shine light on a metal in a vacuum tube and watch electrons fly off — or not. Change the wavelength, intensity, metal and the anode voltage, find the stopping potential and threshold, and plot current against voltage and K_max against frequency.

Interactive virtual lab · no download · works on phones and laptops

Chapter: Dual Nature of Radiation and Matter
For: Class 12 · JEE · NEET
Time: ~12 min

How to use it

1Choose a metal and set the wavelength and intensity of the light.
2Drag the battery voltage from accelerating to retarding and find where the current stops.
3Read the current–voltage graph and the K_max–frequency graph.
4Try a red lamp on sodium and an ultraviolet lamp on zinc.

What to notice

Below the threshold frequency no electrons come out, however bright the light.
K_max = hf − φ: brighter light gives more electrons, not faster ones.
The stopping potential V₀ = K_max / e grows linearly with frequency; the slope of V₀ against f is h/e.
Saturation current depends on intensity, not on frequency.

For teachers

Teach it in 20 minutes

A lesson plan, questions to put to the class, a quick quiz you can project or print, and the formulas behind Photoelectric Effect.

1Hook
~2 min
- Before you switch anything on, ask: “If red light can’t knock electrons out of sodium, will a much brighter red light do it?” Take a show of hands, then test it.
2Demonstrate
~7 min
- Choose a metal and set the wavelength and intensity of the light.
- Drag the battery voltage from accelerating to retarding and find where the current stops.
- Read the current–voltage graph and the K_max–frequency graph.
- Try a red lamp on sodium and an ultraviolet lamp on zinc.
3Pause and ask
~5 min
- Have a student say this in their own words: Below the threshold frequency no electrons come out, however bright the light.
- Have a student say this in their own words: K_max = hf − φ: brighter light gives more electrons, not faster ones.
- Have a student say this in their own words: The stopping potential V₀ = K_max / e grows linearly with frequency; the slope of V₀ against f is h/e.
- Have a student say this in their own words: Saturation current depends on intensity, not on frequency.
4Check
~6 min
- Run the 6-question quiz below: project it and take answers by show of fingers (1–4), or print it as a worksheet.

About the Photoelectric Effect simulation

When light falls on a metal, it can knock electrons out of it — the photoelectric effect. Wave theory predicted that brighter light should give faster electrons and that any colour would work if bright enough. Experiments showed the opposite: below a threshold frequency nothing comes out at all, and above it the electrons' maximum energy depends only on the frequency. Einstein explained it with photons: each carries hf, and one photon frees one electron if hf beats the work function φ.

In this photoelectric effect simulation you choose a metal (from caesium to platinum, with NCERT's work functions), set the wavelength and intensity of the light, and change the anode voltage from accelerating to retarding. Find the stopping potential, see the saturation current follow the intensity, and read the current–voltage and K_max–frequency graphs. It covers Dual Nature of Radiation and Matter in Class 12, JEE and NEET.

Also covers: photoelectric effect, work function, threshold frequency, stopping potential, Einstein's photoelectric equation, photocurrent, saturation current, photon, dual nature of light.

Frequently asked questions

Why does increasing the intensity not increase the kinetic energy of photoelectrons?

Brighter light means more photons, not more energetic ones. Each electron still gets one photon's energy hf, so K_max = hf − φ is unchanged; only the number of electrons (the current) rises.