Change · observe · measure · explain

Photoelectric Effect & Electron Diffraction

Build the paired evidence for wave–particle duality: light transfers energy in photon interactions, while electrons produce diffraction like waves.

Light → particlesPhotoelectric effect

Electrons → wavesDiffraction pattern

Investigation 01

Find the photon threshold

Separate the effect of photon frequency from the effect of beam intensity.

Experimental controls

Set the apparatus

Metal surface 2.28 eV Light wavelength 350 nm Radiation intensity 60%

Show on stage Apparatus labels Measurement guide

Representative work functions vary with surface condition and contamination.

Photon beam · metal surface

Quantum evidence stage

Paused

photon / energy electron wave pattern

Run the experiment, then change wavelength and intensity separately.

One photon · one electron

Live energy budget

Emission

Photon energy, hf3.54 eV

Work function, φ2.28 eV

Maximum Eₖ1.26 eV

Save two runs to compare frequency, intensity, emission rate and maximum kinetic energy.

Recorded readings

Stopping potential against frequency

0 points

λ / nm	f / 10¹⁴ Hz	Vₛ / V
No readings recorded yet.

GradientNeed 3 points

Estimated h—

Threshold f₀—

Fit quality, R²—

Live evidence

Connect observation to model

Photon energy: 3.54 eV
Threshold wavelength: 544 nm
Maximum Eₖ: 1.26 eV
Emission rate: 60% relative

Einstein’s photoelectric equation hf = φ + Eₖ(max)

Evidence board

Observation

Electrons are emitted immediately because each photon carries more energy than the work function.

Conclusion

Energy is transferred in discrete photon interactions rather than being spread continuously across the wavefront.

What to notice

Change intensity without changing wavelength: the emission rate changes, but the maximum electron kinetic energy does not.

Predict before changing it

Move the wavelength above the threshold wavelength. Can any intensity now eject electrons?

Key terms in this experiment

A Level

Misconception check

Intensity changes the number of photons arriving each second, not the energy of each photon.

What the model represents

Particle sizes, colours, positions and rates are schematic. Work functions are representative and depend on surface condition.