Question

An electron enters a chamber in which a uniform magnetic field is present as shown. Ignore gravity.During its motion inside the chamber.

A. The force on the electron remains constant.
B. The kinetic energy of the electrons remains constant.
C. The momentum of the electron remains constant.
D. The speed of the electron increases at a uniform rate.

Answer 1

A uniform magnetic field is one in which the strength and direction are the same at all places. It is represented as a series of parallel lines spaced equally apart. The magnetic field lines point in the same direction as a magnet's north-south pole points.

Complete answer:
When an electron enters a magnetic field, it moves in a uniform circular motion due to the magnetic field's centripetal force. As a result, the electron's speed remains constant.However, its velocity varies along the circle and is not constant. As a result, momentum is not constant.

Similarly, the force acting on the electron is always perpendicular to the velocity, changing its direction.The electron's Kinetic Energy is merely a function of its speed and mass (both of which are constants), hence Kinetic Energy is a constant.

So, the correct option is B.

Note: Many students forget that the inquiry is about electrons, which are negatively charged particles, and thus apply the force of the electric field in the wrong way. Many students forget that the magnetic field has no effect on electron motion since its velocity is in the same direction as the magnetic field's and thus consider its effect when they should not.