$A$ circular loop of radius $r$ of conducting wire connected with a voltage source of zero internal resistance produces a magnetic field $B$ at its centre. If instead, a circular loop of radius $2r$, made of the same material and having the same cross-section, is connected to the same voltage source, what will be the magnetic field at its centre?

In a hydrogen atom, an electron is revolving in an orbit of radius $0.53 \, \text{\AA}$ with $6.6 \times 10^{15} \, \text{rotations/second}$. The magnetic field produced at the centre of the orbit is ....... $Wb/m^2$.

$A$ circular coil carrying current $I$ has a radius $R$ and magnetic field at the centre is $B$. The distance from the centre along the axis of the same coil where the magnetic field will be $\frac{B}{8}$ is

Which of the following graphs shows the variation of magnetic induction $B$ with distance $r$ from a long straight wire carrying current?

Two long parallel wires carrying currents $8 \,A$ and $15 \,A$ in opposite directions are placed at a distance of $7 \,cm$ from each other. $A$ point $P$ is equidistant from both the wires such that the lines joining the point to the wires are perpendicular to each other. The magnitude of the magnetic field at point $P$ is $(\sqrt{2}=1.4)$ $(\mu_0=4 \pi \times 10^{-7} \,T \cdot m/A)$.

The magnetic induction at any point due to a long straight wire carrying a current is