A coil having $N$ $turns$ is wound tightly in the form of a spiral with inner and outer radii $a$ and $b$ respectively. When a current $I$ passes through the coil, the magnetic field at the centre is
$\frac{{{\mu _0}NI}}{b}$
$\frac{{2{\mu _0}NI}}{a}$
$\frac{{{\mu _0}NI}}{{2(b - a)}}\ln \frac{b}{a}$
$\frac{{{\mu _0}{I^N}}}{{2(b - a)}}\ln \frac{b}{a}$
A length $L$ of wire carries a steady current $I$. It is bent first to form a circular plane coil of one turn. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre caused by the same current is
A hollow cylinder having infinite length and carrying uniform current per unit length $\lambda$ along the circumference as shown. Magnetic field inside the cylinder is
Apply Biot-Savart law to find the magnetic field due to a circular current carrying loop at a point on the axis of the loop.
Biot-Savart, law indicates that the moving electrons (velocity $v$) produce a magnetic field $B$ such that