In the figure, what is the magnetic field at the point $O$
$\frac{{{\mu _0}I}}{{4\pi r}}$
$\frac{{{\mu _0}I}}{{4\pi r}} + \frac{{{\mu _0}I}}{{2\pi r}}$
$\frac{{{\mu _0}I}}{{4r}} + \frac{{{\mu _0}I}}{{4\pi r}}$
$\frac{{{\mu _0}I}}{{4r}} - \frac{{{\mu _0}I}}{{4\pi r}}$
Unit of magnetic permeability is
$B _{ X }$ and $B _{ Y }$ are the magnetic field at the centre of two coils of two coils $X$ and $Y$ respectively, each carrying equal current. If coil $X$ has $200$ turns and $20 cm$ radius and coil $Y$ has $400$ turns and $20 cm$ radius, the ratio of $B _{ X }$ and $B _{ Y }$ is
A circular current carrying coil has a radius $R$. The distance from the centre of the coil on the axis where the magnetic induction will be $\frac{1}{8}^{th}$ to its value at the centre of the coil, is
A parallel plate capacitor of area $60\, cm^2$ and separation $3\, mm$ is charged initially to $90\, \mu C$. If the medium between the plate gets slightly conducting and the plate loses the charge initially at the rate of $2.5\times10^{-8}\, C/s$, then what is the magnetic field between the plates ?
In hydrogen atom, an electron is revolving in the orbit of radius $0.53\,{\mathop A\limits^o }$ with $6.6 \times {10^{15}}$ $rotations/second$. Magnetic field produced at the centre of the orbit is.......$wb/{m^2}$