Lab · Beam deflection · e/m

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e/msuccessive determinations ● REC

n = 0

We want to measure the ratio e/m between the charge and the mass of the beam particles. It takes two steps: first the two fields are balanced, and the equilibrium gives the speed v = E/B; then the electric field is switched off and the deflection due to the magnetic field alone is measured.

Accelerating voltage Vₐ2000 V

Plates · voltage V_d0 V

−+

Coils · field B0 mT

−+

Graduated screen · reading

0.0 mm

Measuring bench

Tube geometry: l = 80 mm · d = 25 mm · D = 160 mm

Beam charge: —

The reading on the screen is taken by eye on the graduated scale, so it is rounded to half a millimetre: that is where the uncertainty in the result comes from. If the deflection is too strong the beam hits the plates and never reaches the screen: then V_a must be raised or the fields reduced.

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La Quantistica · Local lab · Ch. 01F. Palma

Simulated laboratory, written in 2026 together with GitHub Copilot: a teaching model, not scientific software.