Current is flowing through a conducting hollow pipe whose area of cross-section is shown in the figure. The value of magnetic induction will be zero at

Two long straight wires are placed along $x$-axis and $y$-axis. They carry current $I_1$ and $I_2$ respectively. The equation of locus of zero magnetic induction in the magnetic field produced by them is

Write formula of magnetic field for ${\rm{x}}\,{\rm{ > }}\,{\rm{ > }}\,{\rm{R}}$.

Current $i$ is passed as shown in diagram. If radius of the circle is a, then the magnetic flux density at the centre $P$ will be:

A wire $A$, bent in the shape of an arc of a circle, carrying a current of $2\, A$ and having radius $2\, cm$ and another wire $B ,$ also bent in the shape of arc of a circle, carrying a current of $3\, A$ and having radius of $4\, cm ,$ are placed as shown in the figure. The ratio of the magnetic fields due to the wires $A$ and $B$ at the common centre $O$ is

The fractional change in the magnetic field intensity at a distance $'r'$ from centre on the axis of current carrying coil of radius $'a'$ to the magnetic field intensity at the centre of the same coil is : (Take $r << a )$