Question

When a charged particle moves only electric or a magnetic field, its speed is $v$ and acceleration is $a$

• A. In a magnetic field, $v$ is constant if the particle moves in a circular path, and variable if it moves in a helical path.
• B. In a magnetic field, $v$ is constant, $a$ may or may not be zero.
• C. In an electric field, $v$ can never remain constant.
• D. In a uniform electric field, $a$ must be constant in magnitude and direction.

Answer 1

Answer: (A)

In a magnetic field, $v$ is constant if the particle moves in a circular path, and variable if it moves in a helical path.

A charged particle moving inside an electric field gets accelerated while in a magnetic field the path of the electron can only be changed.

so, in the magnetic field, if the particle moves in a circular path, its speed remains constant while in a helical path, its speed is variable.