$A$ vertical wire kept in the $Z-X$ plane carries a current from $Q$ to $P$ (see figure). The magnetic field due to the current will have the direction at the origin $O$ along

If a wire of length $L$ forms a loop of radius $R$ and has $n$ turns,find the magnetic field at the center of the loop if the current flowing in the loop is $I$.

Two identical long parallel wires carry currents $I_1$ and $I_2$ such that $I_1 > I_2$. When the currents are in the same direction,the magnetic field at a point midway between the wires is $6 \times 10^{-6} \ T$. If the direction of $I_2$ is reversed,the field becomes $3 \times 10^{-5} \ T$. The ratio $\left(\frac{I_1}{I_2}\right)$ is-

What is the ratio of the magnetic field at point $O$ in the given figures?

The magnetic field at the origin due to the current $I$ flowing in the wire is -

Two concentric rings are kept in the same plane. The number of turns in each ring is $25$. Their radii are $50 \text{ cm}$ and $200 \text{ cm}$,and they carry electric currents of $0.1 \text{ A}$ and $0.2 \text{ A}$ respectively in mutually opposite directions. The magnitude of the magnetic field produced at their centre is . . . . . . $\text{T}$.