According to Biot-Savart law magnetic field ...... at point of axis of wire.

An electron revolves around nucleus with rotational frequency $'f'$ in circular orbit, due to this magnetic induction produced at nucleus position is $'B'$ then radius of circular orbit is directly proportional to

A long thin walled pipe of radius $R$ carries a current $I$ along its length. The current density is uniform over the circumference of the pipe. The magnetic field at the center of the pipe due to quarter portion of the pipe shown, is

The current of $5 \mathrm{~A}$ flows in a square loop of sides $1$ $\mathrm{m}$ is placed in air. The magnetic field at the centre of the loop is $\mathrm{X} \sqrt{2} \times 10^{-7} \mathrm{~T}$. The value of $\mathrm{X}$ is____.

Magnetic field due to $0.1\, A$ current flowing through a circular coil of radius $0.1\, m$ and $1000$ $turns$ at the centre of the coil is

Two parallel long current carrying wire separated by a distance $2 \mathrm{r}$ are shown in the figure. The ratio of magnetic field at $\mathrm{A}$ to the magnetic field produced at $C$ is $\frac{x}{7}$. The value of $x$ is $\qquad$