When a proton is released from rest in a room, it starts with an initial acceleration $a_0$ towards west. When it is projected towards north with a speed $v_0$ it moves with an initial acceleration $3a_0$ towards west. The electric and magnetic fields in the room are

An electron moving in a circular orbit of radius $r$ makes $n$ rotations per second. The magnetic field produced at the center has a magnitude, 

A wire-carrying current $I$ has the shape as shown in the adjoining figure. Linear parts of the wire are very long and parallel to $X$-axis while a semicircular portion of the radius $R$ is lying in $Y-Z$ plane, Magnetic field at a point $O$ is

A long straight wire of radius $a$ carries a steady current $I$. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields $B$ and $B^{\prime}$ at radial distances $\frac{a}{2}$ and $2a$  respectively, from the axis of the wire is

A square loop $ABCD$ carrying a current $i$, is placed near and coplanar with a long straight conductor $XY$ carrying a current $I$, the net force on the loop will be

A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is $B$ . It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of $n$ turns will be