Two thick wires and two thin wires, all of the same materials and same length form a square in the three different ways $P$, $Q$ and $R$ as shown in fig with current connection shown, the magnetic field at the centre of the square is zero in cases

A current of $0.1\, A$ circulates around a coil of $100$ $turns$ and having a radius equal to $5\,cm$. The magnetic field set up at the centre of the coil is ($\mu_0 = 4\pi \times 10^{-7} weber/amp-metre$)

Magnetic field due to a ring having $n$ turns at a distance $x$ on its axis is proportional to (if $r$ = radius of ring)

The magnitude of magnetic induction at mid-point $O$ due to current arrangement as shown in Fig will be

A charge $q$ coulomb moves in a circle at $n$ revolutions per second and the radius of the circle is $r$ metre; then magnetic field at the centre of the circle is

In hydrogen atom, an electron is revolving in the orbit of radius $0.53\,{\mathop A\limits^o }$ with $6.6 \times {10^{15}}$ $rotations/second$. Magnetic field produced at the centre of the orbit is.......$wb/{m^2}$