A charged particle moving along the +x-axis enters a uniform $\vec { B }$ field pointing along the +z-axis.A uniform electric field is also present.Due to the combined effect of both fields,the particle does not change its velocity.What is the direction of the electric field?

Question

Quizplus · Accepted Answer

We know that a charged particle moving in a magnetic field experiences a force perpendicular to its velocity given by F = qvB where q is the charge of the particle, v is its velocity and B is the magnetic field. As the particle does not change its velocity, it follows that there must be an electric force that balances the magnetic force. The electric force is given by Fe = qE where E is the electric field. As the particle is moving only along the x-axis and the magnetic field is along the z-axis, the magnetic force will be in the y-direction. Therefore, to balance this force, the electric field must also be along the y-axis. Thus, the answer is B) along the +y-axis.

A Charged Particle Moving Along the +X-Axis Enters a Uniform B⃗\vec { B }B

A Charged Particle Moving Along the +X-Axis Enters a Uniform $\vec { B }$