Electron diffraction
Nothing movesElectrons accelerated through a voltage and diffracted by graphite: the rings move as 1/√V, which is de Broglie’s λ = h/p made visible.
Nuclear & quantum — Radioactive decay, the absorption of radiation, photons, and energy levels in the atom.
Experiments already set up on it
Measuring h from a ring
The headline: the ring radius against 1/√V is straight, and h is in it.
- λ = h/p, and p = √(2meV)
- So the ring radius goes as 1/√V
- Electrons diffract, which means a particle has a wavelength
Why there are two rings
Two spacings in graphite, so two rings — and the closer planes give the wider one.
- A smaller spacing diffracts more, so the tighter planes make the bigger ring
- The ratio of the radii is set by the ratio of the spacings, not by the voltage
What you can measure
Each of these can be recorded over time, aggregated over a run, or read at the moment something happens — through an instrument that carries its own uncertainty.
- de Broglie wavelengthλ (pm)
- Momentump (kg m/s)
- Speed, as a fraction of cv/c
- Bragg angleθ (°)
- Radius of the ringr (mm)
- 1/√VinvsqV
- Spacing of the planesd (m)
What you can change
Any of these can be the thing you vary, and every combination of the ones you choose is run as its own trial.
- Accelerating voltageV (V)
- Target to screenL (m)
The equations behind it
What electron diffraction is built on. Every one of these is in the lab's formula reference too, where it copies straight into a write-up.
Quantum physics
- Energy of a photon
- Photoelectric equation — Φ is the work function.
- Work function and threshold frequency
- Stopping voltage
- de Broglie wavelength
- Energy levels of hydrogen
- Heisenberg uncertainty, position and momentum
- Heisenberg uncertainty, energy and time
- The electronvolt
Also in Nuclear & quantum
Radioactive decay
A source counted with a Geiger tube, decay by decay, with the √N scatter of real counting statistics and a background that does not decay.
Absorption of radiation
Alpha, beta and gamma through absorbers of your choosing: only one of the three is absorbed exponentially, and the counter still does not subtract the background.
Photoelectric effect
Light on a metal plate and a retarding voltage turned up until the current stops: the stopping voltage is found rather than calculated, and brightness changes nothing about it.
Muon decay & time dilation
Cosmic-ray muons counted at any altitude you like: far more arrive than a muon’s lifetime allows, and only a slow-running clock accounts for it.
Atomic spectra
Hydrogen through a grating spectrometer: each line is an electron falling between two levels, and a graph of them gives the Rydberg constant.
Rutherford scattering
Alpha particles onto a thin foil, counted at an angle: the 1/sin⁴(θ/2) law is what a point nucleus gives, and a head-on alpha says how small it is.