Question

An electron travelling west to east enters a chamber having a uniform electrostatic field in the north to south direction. Specify the direction in which a uniform magnetic field should be set up to prevent the electron from deflecting from its straight-line path.

Answer 1

The force on the electron due to the electric field is south to north. To oppose this the force due to the magnetic field should be to the south. For this B is to be applied in the downward direction.