If a positive ion is moving, away from an observer with same acceleration, then the lines of force of magnetic induction will be

A particle of mass $m$ and charge $q$ is in an electric and magnetic field given by

$\vec E = 2\hat i + 3\hat j ;\, B = 4\hat j + 6\hat k$

The charged particle is shifted from the origin to the point $P(x = 1 ;\, y = 1)$ along a straight path. The magnitude of the total work done is

Show that a force that does no work must be a velocity dependent force.

A negative charge is coming towards the observer. The direction of the magnetic field produced by it will be (as seen by observer)

Assertion : A proton and an alpha particle having the same kinetic energy are moving in circular paths in a uniform magnetic field. The radii of their circular paths will be equal.

Reason : Any two charged particles having equal kinetic energies and entering a region of uniform magnetic field $\overrightarrow B $ in a direction perpendicular to $\overrightarrow B $, will describe circular trajectories of equal radii.