Consider the motion of a positive point charge in a region where there are simultaneous uniform electric and magnetic fields E = E_0 j and B = B_0 j. At time t = 0, this charge has velocity v in the x-y plane, making an angle θ with the x-axis. Which of the following option(s) is(are) correct for time t > 0 ?

JEE Advanced 2012 Physics question

Consider the motion of a positive point charge in a region where there are simultaneous uniform electric and magnetic fields and . At time t = 0, this charge has velocity in the x-y plane, making an angle θ with the x-axis. Which of the following option(s) is(are) correct for time t > 0 ?

(A)If θ = 0°, the charge moves in a circular path in the x-z plane.
(B)If θ = 0°, the charge undergoes helical motion with constant pitch along the y-axis.
(C)If θ = 10°, the charge undergoes helical motion with its pitch increasing with time, along the y-axis.Correct
(D)If θ = 90°, the charge undergoes linear but accelerated motion along the y-axis.Correct

Answer: (C),(D)

Solution

The magnetic field (along y) affects only the velocity component perpendicular to y, producing circular motion in the x-z plane; the electric field (also along y) accelerates the charge uniformly along y. (A), (B) For θ = 0° the initial velocity is along x: the charge circles in the x-z plane while accelerating along

See the full step-by-step solution

Create a free account to read the complete working, and practise questions like this in a timed test.

Create a free account

Question ID VK-026017