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:

The magnetic force acts only on moving charges. A stationary charge experiences no force from a static magnetic field.

Answer 1

The Correct Option is A

Step 1: Recall the formula for magnetic force on a charged particle.
The magnetic force (Lorentz force) experienced by a charged particle moving in a magnetic field is given by the formula: \[ \vec{F} = q(\vec{v} \times \vec{B}) \] Where: - \( \vec{F} \) is the magnetic force vector. - \( q \) is the charge of the particle (for an electron, \( q = -e \)). - \( \vec{v} \) is the velocity vector of the particle. - \( \vec{B} \) is the magnetic field vector.

Step 2: Apply the condition for a stationary electron.
The problem states that the electron is stationary. This means its initial velocity is zero. \[ \vec{v} = 0 \]

Step 3: Calculate the magnetic force.
Substitute \( \vec{v} = 0 \) into the Lorentz force equation: \[ \vec{F} = q(0 \times \vec{B}) = 0 \] Since the cross product of the zero vector with any other vector is the zero vector, the magnetic force on the stationary electron is zero.

Step 4: Conclusion.
According to Newton's first law, an object at rest stays at rest if no net force acts on it. Since the magnetic force on the stationary electron is zero, it will not accelerate and will continue to remain stationary.

Final Answer: (A) remains stationary