How to investigate
Start with a prepared experiment. Install tools using Apparatus.
Select a part on the bench or in the selector; use Adjust for
precise settings. Source and filter slide along separate rail
stations. Drag the diffraction screen to change its distance; drag
the radius cursor on the face-on screen to measure a ring.
With the bench focused, Space runs or pauses, left/right arrows move
a selected rail part (Shift for fine movement), Delete removes it,
and Escape cancels a drag. Fit bench resets the view; drag empty
space to pan after zooming.
For Planck’s constant: use the same metal at several wavelengths.
Reduce the signed collector voltage in 0.01 V steps until the
current first becomes zero, then record stopping voltage. The first
zero step brackets the stopping potential to 0.01 V. A fit appears
after three distinct frequencies.
For diffraction: measure the inner-ring radius from the centre using
the ruler. Keep target–screen distance fixed while varying voltage.
The notebook estimates λ ≈ dR/L with d = 0.213 nm.
Model, instruments & limits
One photon can release at most one electron. E = hf and KEmax = hf −
φ. Intensity is relative photon arrival rate; changing wavelength at
fixed rate changes optical power. Representative work functions
depend on surface condition. The lamp beam is collimated: sliding it
along the rail does not introduce inverse-square dimming.
The current curve is a steady-state teaching approximation with a
spread of electron energies and incomplete collection at zero bias.
Its tiny drawn particle sample illustrates events, not the number of
electrons per second. Meter readings update immediately; they do not
count the visible particles. Electron speeds use a fixed display
scale with v ∝ √KE. A field acts on electrons already in flight. A
changing field can do additional work. Optical photons keep their
emission energy.
The nanoammeter resolves 0.001 nA; the voltmeter resolves 0.01 V.
Stopping is judged using the underlying ideal current, not a rounded
apparent zero. Missing instruments give an unavailable reading. Time
on the bench is illustration time.
Diffraction uses non-relativistic electrons at 1–6 kV, graphite
spacings 0.213 and 0.123 nm, first-order Bragg scattering and a flat
screen. R = L tan(2θ), 2d sin θ = λ, λ = h/√(2meV). Single-crystal
spots are qualitative; use polycrystal rings for radius
measurements. Screen brightness is schematic, not a calibrated
intensity profile.
SI constants · NIST
·
Electron diffraction · LMU
