Read the following passage and answer the questions.
A parallel plate capacitor has two plates, each of area 0.10 m2, with air between them. A source charges the capacitor. The current in the connecting wires stays constant at 0.885 mA. Take \(\varepsilon_0=8.85\times10^{-12}\ \mathrm{C^{2}\,N^{-1}\,m^{-2}}\). A student draws a circular loop of radius \(r\) around one connecting wire, close to a plate. The plane of the loop is perpendicular to the wire. She marks a point P on the loop. She wants to find the magnetic field at P with the help of Ampere’s law. For this, she takes two surfaces that have the loop as their rim (edge). The first is a flat circular disc, and the wire passes through it. The second is a pot-shaped surface. Its bottom lies in the gap between the plates, and it does not touch the wire anywhere.
While the capacitor is being charged, the current that crosses the pot-shaped surface is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → the displacement current only
A conduction current is a flow of charges, as in the connecting wires. No charge flows across the gap between the plates, but the electric field in the gap changes with time.
Option (1) the displacement current only — Correct. The bottom of the pot lies in the gap, where the electric field keeps growing. The changing electric flux there gives a displacement current \( i_d=\varepsilon_0\,d\Phi_E/dt \), equal to \( i \).
Option (2) the conduction current only — Incorrect. The conduction current flows in the wire. The pot-shaped surface does not touch the wire anywhere, so this current does not cross it.
Option (3) both the conduction current and the displacement current — Incorrect. There is no conduction current in the gap between the plates. The surface is crossed by the displacement current alone.
Option (4) neither the conduction current nor the displacement current — Incorrect. This is what Ampere’s law without the displacement current assumes. It leaves out the changing electric field between the plates.
NCERT (2026-27):
Displacement Current – “On the other hand, inside the capacitor, there is no conduction current, i.e., ic = 0, and there is only displacement current, so that id = i.”