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# A charged particle is moving in a region of uniform magnetic field and a parallel uniform electric field. At some time the velocity of the particle is perpendicular to the magnetic field. The trajectory of the particle will be

$\begin {array} {1 1} (a)\;Straight\: line & \quad (b)\;Circle \\ (c)\;Helix\: with\: uniform\: pitch & \quad (d)\;Helix\: with\: non-uniform\: pitch \end {array}$

The speed along the axis of the helix is not constant due to the presence of electric field.
The perpendicular component is unaltered and hence the motion is helix with a non-uniform pitch
Ans : (d)