Question

An electron of charge \( e \) moves parallel to uniform lines of force in a magnetic field \( B \) with velocity \( v \). The force acting on the electron is:

• A. \( evB \)
• B. \( \frac{ev}{B} \)
• C. \( 0 \)
• D. \( \frac{Bv}{e} \)

Hint:

Magnetic force on charge: \[ \mathbf{F} = q \mathbf{v} \times \mathbf{B} \quad \Rightarrow \quad F = q v B \sin \theta, \] which is zero when \( \theta = 0^\circ \) or \( 180^\circ \).

Answer 1

The Correct Option is C

The magnetic force on a charged particle is given by: \[ \mathbf{F} = q(\mathbf{v} \times \mathbf{B}). \] If the velocity \( \mathbf{v} \) is parallel to the magnetic field \( \mathbf{B} \), then the cross product is zero: \[ \mathbf{F} = 0. \] Thus, the force acting on the electron is zero.