MASS SPECTROMETER
m = qBr/v — mass from a photograph: the roundtrip returns carbon-12 bitwise.
Use the simulation above to change the variables and play through the guided stages. The explanation below describes the default starting values; the simulation updates its explanation as you experiment.
Setup
A classroom model sends singly charged, velocity-selected isotope beams through a magnetic field. It uses tabulated neutral atomic masses as an approximation for ion masses and reports the size of the neglected electron-mass and relativistic corrections.
One radius per mass
The nonrelativistic radius is mv/qB, so each isotope lands at its own spot two radii from the slit. Canvas and result values are shown to three significant figures, consistent with this simplified neutral-mass model.
The inversion
Run the model formula backwards: m = qBr/v. Its bitwise roundtrip and radius-ratio checks establish internal code consistency, not sixteen-digit experimental accuracy; the physical approximation floor is stated alongside them.
Sweeping the field
The sweep runs the field from weak to strong: both half-circles shrink together, the landing spots crowd toward the slit — but the RATIO of the radii never moves, because the masses never move. A stronger magnet buys a smaller instrument, not a different answer.
Audit
Audited at honest precision: carbon radii 2.49 and 2.70 cm, radius gap 2.08 mm. Internal identities are tested separately from model accuracy, with the neutral-to-ion mass shift and relativistic momentum correction quantified in ppm.