A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set up in a chamber. A charged particle enters the chamber and travels undeflected along a straight path with constant speed. What can you say about the initial velocity of the particle?
A charged particle enters an environment of a strong and non-uniform magnetic field varying from point to point both in magnitude and direction, and comes out of It following a complicated trajectory. Would its final speed equal the initial speed if it suffered no collisions with the environment? An electron travelling west to east enters a chamber baving a uniform electrostatic field in 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.

Explanation

The force on a charged particle moving in a magnetic field is F+qxB) - qvB sin 0. If `theta = 0^@ or 180^@`, force is zero and the particle goes undeflected. So its initial velocity is parallel to B b A space fixed magnetic field cannot do work on moving charge and hence the speed remains the same (so also KE). The force on the electron due to electric field is outh to north. To oppose this the force due to magnetic field should be to south For this B is to be applied in the downward direction.