The source of an electromagnetic wave can be a charge

What was the primary difficulty in establishing the wave theory of light,and who explained it?

The charge on a capacitor varies with time as $q = q_0 \sin(2\pi nt)$. What is the displacement current produced in the dielectric of the capacitor?

The figure shows a capacitor made of two circular plates,each of radius $12 \; cm$,separated by $5.0 \; cm$. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and equal to $0.15 \; A$.
$(a)$ Calculate the capacitance and the rate of change of potential difference between the plates.
$(b)$ Obtain the displacement current across the plates.
$(c)$ Is Kirchhoff's first rule (junction rule) valid at each plate of the capacitor? Explain.

The source of a time-varying magnetic field may be:
$(A)$ A permanent magnet
$(B)$ An electric field changing linearly with time
$(C)$ Direct current
$(D)$ A decelerating charged particle
$(E)$ An antenna fed with a digital signal
Choose the correct answer from the options given below:

The electric field through an area of $2 \ m^2$ varies with time as shown in the graph. The greatest displacement current through the area is at $t = ..... \ \mu s$.