Question

A proton enters a region in which there are both electric and magnetic fields. The fields are both uniform and their directions are mutually perpendicular. The velocity of the proton does not change as it moves through this region. Which of the following is a possible explanation for this observation? Question 2 options: a) The proton's velocity is perpendicular to both the electric and magnetic fields and has a magnitude equal to B/E. b) The proton's velocity is parallel to the electric field and has a magnitude E/B. c) The proton's velocity is perpendicular to both the electric and magnetic fields and has a magnitude equal to E/B. d) The situation described cannot happen. e) The proton's velocity is parallel to the magnetic field.

Answer 1

Given is:-

Electric Field E and Magnetic Field B are uniform and perpendicular to each other.

The velocity of proton is constant that means Net force acting on proton is zero and therefore it's acceleration is zero.

This is only possible when electric field and magnetic field and motion of the proton are mutually perpendicular to each other and magnetich force is equal and opposite to electric force

therefore or   

Hence,

The proton's velocity is perpendicular to both the electric and magnetic fields and has a magnitude equal to E/B

Option -C is correct answer