Dinglo Photoelectric Effect Virtual Laboratory

Interactive apparatus

Optical bench and photoelectric tube

Photon energy- eV

Threshold statusLamp off

Measured current0.00 pA

Theoretical stopping potential- V

Switch on the source, allow it to stabilise, choose a wavelength, calibrate the current meter, and open the shutter.

Technique

Practical checklist

Live model

What the apparatus is doing

Einstein photoelectric equation

K_max = hf − φ

Frequency- Hz

Maximum kinetic energy- eV

Saturation current- pA

Collection fraction- %

The lamp is currently off.

Experimental controls

Configure the apparatus

Light and optics

Wavelength filter

Intensity 60% Aperture

Source distance 25 cm

Phototube

Cathode material

Nominal work function - eV Assessment mode hides this parameter.

Electrical controls

Anode potential 0.000 V

Current range

Calibration mode

Close the shutter and enable calibration mode before zeroing.

Measurement

Zero-current criterion 1.0 pA

Raw data

Current-voltage readings

#	Time	λ (nm)	f (10¹⁴ Hz)	Intensity	Aperture	Bias (V)	Current (pA)	Range

Raw readings are preserved exactly as recorded. Delete only clearly invalid measurements and document why in your notes.

Graph 1

Photocurrent versus anode potential

Record at least three readings to display the current-voltage curve.

Processed data

Stopping-potential dataset

λ (nm) V_s (V) u(V_s) (V)

#	λ (nm)	f (10¹⁴ Hz)	V_s (V)	u(V_s)	Method

Graph 2

Stopping potential versus frequency

Add at least three stopping-potential results at different wavelengths.

Laboratory notebook

Observations, anomalies and interpretation

Foundation

Photoelectric-effect theory

When electromagnetic radiation strikes a suitable metal surface, electrons may be emitted. Each photon carries energy E = hf = hc/λ. An electron can escape only when the photon energy exceeds the material work function, φ.

Photon energyE = hf = hc/λ

Maximum kinetic energyK_max = hf − φ

Stopping potentialeV_s = hf − φ

Linear formV_s = (h/e)f − φ/e

Predictions to test

Below the threshold frequency, no photoelectrons are emitted, regardless of intensity.
At fixed frequency, increasing intensity increases photocurrent and saturation current.
At fixed frequency, intensity should not materially change the stopping potential.
Increasing frequency increases maximum kinetic energy and stopping potential.
A graph of V_s against frequency should be linear, with slope h/e.

Instrument realism in this simulator

The virtual meter includes dark current, a session-specific zero offset, random noise, finite resolution and overload. The source includes warm-up drift, aperture scaling, inverse-square distance scaling and wavelength-dependent response. These effects are deliberately modest so that the correct physics remains recoverable through good technique.

Readiness check

Pre-laboratory quiz

1. Increasing light intensity above threshold mainly increases: The energy of each photon The number of emitted electrons The work function

2. The stopping potential is the retarding potential at which: The photocurrent reaches a practical zero threshold The lamp switches off The cathode melts

3. The slope of V_s versus f is: e/h h/e φ/e

4. Before zeroing the current meter, the shutter should be: Open Closed

Practical programme

Recommended investigations

Investigation AThreshold frequency

Keep intensity fixed, vary wavelength and identify the onset of emission.

Investigation BIntensity dependence

Use one wavelength, vary aperture or intensity, and compare saturation currents and stopping potentials.

Investigation CCurrent-voltage curves

Sweep from retarding to accelerating bias and identify stopping, transition and saturation regions.

Investigation DPlanck constant

Measure stopping potential for at least four wavelengths and fit V_s against frequency.

Photoelectric Effect