alleryCyclotrons are not used to accelerate electrons because
AElectrons have negative charge
BElectron mass grows too fast with energy
CMagnetic field cannot deflect electrons
DElectrons spin too rapidly for resonance
Answer & Solution
Correct answer: B. Electron mass grows too fast with energy
1. Cyclotron operation depends on a constant frequency f = qB/(2πm).
2. As electrons gain energy, their relativistic mass m grows rapidly because the rest mass is very small.
3. The cyclotron frequency therefore drifts, breaking resonance with the AC accelerating voltage.
4. Heavier ions tolerate higher energies before relativistic effects matter; for electrons, betatrons or synchrotrons are used instead.
_Source: syllabus Physics Ch 4 "Moving Charges and Magnetism", §4.4.2_
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