Choose the correct answer from the options given below :
(Image)
$(B)$ magnetic field due to a current carrying wire for $\mathrm{x}<\mathrm{a}$ :
$\mathrm{B}=\frac{\mu_0 \mathrm{ir}}{2 \pi \mathrm{a}^2}$
(Image)
$(C)$ magnetic field due to a current carrying wire for $x>a$ :
$B=\frac{\mu_0 i}{2 \pi a}$
(Image)
$(D)$ magnetic field inside solenoid varies as:
$(A)$ In the region $0 < r < R$, the magnetic field is non-zero.
$(B)$ In the region $R < r < 2 R$, the magnetic field is along the common axis.
$(C)$ In the region $R < r < 2 R$, the magnetic field is tangential to the circle of radius $r$, centered on the axis.
$(D)$ In the region $r > 2 R$, the magnetic field is non-zero.

$(i)$ an equilateral triangle of side $'a'.$
$(ii)$ a square of side $'a'.$
The magnetic dipole moments of the coil in each case respectively are:
$(i)$ Electrons $(ii)$ Protons $(iii)$ $H{e^{2 + }}$ $(iv)$ Neutrons
The emission at the instant can be
