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 $v = \frac{E}{B} = \frac{20}{0.5} = 40\text{ ms}^{-1}$.

Leave a Reply

Your email address will not be published. Required fields are marked *

Similar Practice Questions

Explore conceptually related problems to test your knowledge.

1. 20. A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from: (2018)
2. Assertion (A): A charged particle moves perpendicular to magnetic field. Its kinetic energy will remain constant but momentum changes. Reason (R): Magnetic force acts perpendicular to velocity of particle.  
3. Assertion (A): If a uniform current carrying loop is placed in uniform magnetic field perpendicular to plane of loop. Tension or compression is created in loop. Reason (R): Net force on any closed loop in uniform magnetic field is zero.  
4. Assertion (A): Work done by magnetic force on any moving charge is zero. Reason (R): Magnetic force is perpendicular to velocity.  
5. A material suitable for making electromagnets should have