Q. A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected in the region such that its velocity is pointed along the direction of fields, then the electron
A) Will turn towards left of direction of motion
B) Will turn towards right of direction of motion
C) Speed will decrease
D) Speed will increase
Explanation
[Solution from source] Since the velocity is parallel to B, the magnetic force qv × B is zero and there is no sideways turning. The electron's charge is negative, so the electric force is opposite to E, i.e. opposite to its velocity, and it decelerates, so its speed decreases. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.