Question

When a magnetic field is applied on a stationary electron, it

• A. remains stationary
• B. spins about its own axis
• C. moves in the direction of the field
• D. moves perpendicular to the direction of the field
• E. moves opposite to the direction of the field

Hint:

Magnetic fields do not perform work on charges because the force is always perpendicular to velocity. If velocity is zero, there is no force at all.

Answer 1

The Correct Option is A

To solve the question of what happens to a stationary electron when a magnetic field is applied, we need to understand the basic principles of electromagnetism pertaining to charged particles in magnetic fields.

According to the Lorentz force law, the force \(\mathbf{F}\) experienced by a charged particle with charge \(q\), moving with velocity \(\mathbf{v}\) in a magnetic field \(\mathbf{B}\), is given by:

\[\mathbf{F} = q(\mathbf{v} \times \mathbf{B})\]

Where:

• \(\mathbf{F}\) is the magnetic force.
• \(q\) is the charge of the particle (for an electron, q = -e).
• \(\mathbf{v}\) is the velocity of the particle.
• \(\mathbf{B}\) is the magnetic field.
• \(\times\) represents the cross product.

Since the electron is stationary, its velocity \(\mathbf{v}\) is zero. Thus, the cross product \(\mathbf{v} \times \mathbf{B} = \mathbf{0}\), and therefore, the force \(\mathbf{F}\) experienced by the electron is zero.

This means that the electron will not be subjected to any magnetic force if it is not moving, and consequently, it will remain stationary. Therefore, the correct answer is that the electron remains stationary.

Conclusion

When a magnetic field is applied to a stationary electron, it remains stationary. The application of a magnetic field does not influence the motion of a stationary charged particle since the force depends on the velocity.