One metre length of wire carries a constant current. The wire is bent to form a circular loop. The magnetic field at the centre of this loop is $B$. The same is now bent to form a circular loop of smaller radius to have four turns in the loop. The magnetic field at the centre of this new loop is

An electron moves in a circular orbit with a uniform speed $v$. It produces a magnetic field $B$ at the centre of the circle. The radius of the circle is proportional to

A closely wounded circular coil of radius $5\,cm$ produces a magnetic field of $37.68 \times 10^{-4}\,T$ at its center. The current through the coil is $......A$. [Given, number of turns in the coil is $100$ and $\pi=3.14]$

An element $d l=d x \hat{l}$ (where, $d x=1\, cm$ ) is placed at the origin and carries a large current $i=10 A$. What is the magnetic field on the $Y$ -axis at a distance of $0.5\, m$ ?

In a hydrogen atom, an electron moves in a circular orbit of radius $5.2 \times {10^{ - 11}}\,m$ and produces a magnetic induction of $12.56\, T$ at its nucleus. The current produced by the motion of the electron will be (Given ${\mu _0} = 4\pi \times {10^{ - 7}}\,Wb/A - m)$

The magnetic induction at a point $P$ which is distant $4\, cm$ from a long current carrying wire is ${10^{ - 8}}\,Tesla$. The field of induction at a distance $12\, cm $ from the same current would be