question_answer 17)

Answer the following questions (a) A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set tip 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? (b) 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? (c) An electron travelling west to east enters, a chamber having 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 deflection from its straight line path.  

Answer:

(a) The particle goes undeflected so it is not experiencing magnetic force.Using. It is clear that the initial velocity is either parallel or anti-parallel to i.e., is either or .                 (b) Yes, the final speed is equal to the initial speed because the magnetic force can change the direction of  but the magnitude of  cannot be changed by it.                 (c) The electron has a tendency to move towards north because of the positive polarity of the field existing there.                 To keep the electron undeflected, the magnetic force should act towards south. Using Fleming's left hand rule and considering the conventional direction of flow of charge from east to west we get direction of magnetic field along the vertical in downward direction.