# Circular motion of ions in a magnetic field

Electricity and Magnetism Level 3

A beam of ions, each of charge $$–3.20 \times 10^{–19}\text{ C}$$ and travelling at a speed of $$1.2 \times 10^5\text{ m s}^{–1}$$, enters a region where a uniform magnetic field of flux density $$2.4 \times 10^{-2}\text{ T}$$ acts normally to the original direction of the beam, as shown below.

When the ions are in the magnetic field, they are deflected and they travel in a circular path of radius $$0.390\text{ m}$$. What is the nucleon number of the nuclei of the ions in the beam?

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