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 electron remains constant.
• C. The momentum of the electron remains constant.
• D. The speed of the electron increases at a uniform rate.

Answer 1

The correct option is B The kinetic energy of the electron remains constant.

When the Electron enters the magnetic field, it exhibits uniform circular motion, where the centripetal force is due to the magnetic field.

Thus, the speed of the electron remains constant. However, its velocity changes the direction along the circle and is not constant. So, momentum is not a constant.

Similarly, Force acting on the electron is always perpendicular to the velocity and thus also changes its direction.

The Kinetic Energy of the electron is only a function of its speed and mass (both of which are constants) and thus, Kinetic Energy is a constant.