Rankers Physics

Force Acting on Moving Charges: Practice Problem & Solution

A beam of electrons is moving with constant velocity in a region having electric and magnetic fields of strength $20\text{ Vm}^{-1}$ and $0.5\text{ T}$ at right angles to the direction of motion of the electrons. What is the velocity of the electrons? (1996)
$8\text{ ms}^{-1}$
$5.5\text{ ms}^{-1}$
$20\text{ ms}^{-1}$
$40\text{ ms}^{-1}$

Solution Explained:

To solve this problem, we apply the core principles of Force Acting on Moving Charges. Understanding the underlying formula is key to arriving at the correct answer below:

For undeflected particle motion in perpendicular fields, magnetic force balances electric force ($qE = qvB$).
Thus, velocity $v = \frac{E}{B} = \frac{20}{0.5} = 40\text{ ms}^{-1}$.

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