Show that the magnetic field $B$ at a point in between the plates of a parallel-plate capacitor during charging is $B = \frac{{\mu _0 \epsilon _0 r}}{2} \cdot \frac{{dE}}{{dt}}$ (symbols have their usual meanings).

Write the meaning of the equation $i = i_c + i_d$.

The displacement current of $4.425 \,\mu A$ is developed in the space between the plates of a parallel plate capacitor when the voltage is changing at a rate of $10^{6} \,V s^{-1}$. The area of each plate of the capacitor is $40 \,cm^{2}$. The distance between the plates of the capacitor is $x \times 10^{-3} \,m$. The value of $x$ is ................ (Permittivity of free space,$\varepsilon_{0} = 8.85 \times 10^{-12} \,C^{2} N^{-1} m^{-2}$)

$A$ long straight cable of length $l$ is placed symmetrically along $z-$ axis and has radius $a (a << l)$. The cable consists of a thin wire and a co-axial conducting tube. An alternating current $I(t) = I_0 \sin(2\pi \nu t)$ flows down the central thin wire and returns along the co-axial conducting tube. The induced electric field at a distance $s$ from the wire inside the cable is $\vec{E}(s,t) = \mu_0 I_0 \nu \cos(2\pi \nu t) \ln(s/a) \hat{k}$.
$(i)$ Calculate the displacement current density inside the cable.
$(ii)$ Integrate the displacement current density across the cross-section of the cable to find the total displacement current $I_d$.
$(iii)$ Compare the conduction current $I_0$ with the displacement current $I_d$.

Write inferences from Maxwell's equations.

$A$ circular parallel plate capacitor of radius $R$ and spacing $d$ is being charged by a constant current $I_D$. Find the magnetic field between the plates at a distance $r$ from the axis,where $r > R$.