A rectangular coil can rotate in a magnetic field. The two ends of the coil are soldered respectively to the two halves of a commutator. Two carbon brushes are made to press lightly against the commutator and when these are connected in a circuit with a battery and a rheostat, the coil rotates. This is a description of
A particle of charge q and mass m moving with a velocity v enters a uniform magnetic field of strength B in the direction of the field. The force on the particle is
