Question

Study the following three diagrams in which the entry of an electron in a magnetic field is shown. Identify the case in which the magnetic force experienced by the electron is (i) maximum, and (ii) minimum. Give reason for your answers in each case.

Answer 1

Fleming’s left-hand rule is used to find the direction of force acting on a current-carrying conductor placed in a magnetic field.

(i) The magnetic force experienced by the electron is maximum in case (A).

Reason: Because here the direction of motion of the electron is at a right angle (90°) to the magnetic field (B).

Mathematical expression:

F = qvB sin θ

∵ θ = 90°, sin 90° = 1

F = qvB (maximum)

(ii) The magnetic force experienced by the electron is minimum (zero) in case (C).

Reason: Because here the direction of motion of the electron is along (parallel) to the direction of the magnetic field (B).

Mathematical expression:

∵ θ = 0° (or 180°)

F = qvB sin 0°

F = 0 (minimum or zero)