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.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): While the capacitor is being charged, a magnetic field exists at a point between its plates.
Reason (R): When a conducting wire has a steady electric field in it, the displacement current in the wire is zero.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
Assertion (A) While the capacitor is being charged, a magnetic field exists at a point between its plates. — True. The electric field between the plates grows with time. This changing field gives a displacement current, and the displacement current produces a magnetic field there.
Reason (R) When a conducting wire has a steady electric field in it, the displacement current in the wire is zero. — True. The displacement current is \( \varepsilon_0\,d\Phi_E/dt \). A steady field does not change with time, so this term is zero.
Why Reason (R) does not explain Assertion (A)?
The magnetic field between the plates comes from the displacement current in the gap. There the electric field changes with time.
R is about a steady field inside a wire, where the displacement current is zero. It says nothing about the gap between the plates, and A is about the gap.
NCERT (2026-27):
Displacement Current – “For example, a magnetic field (say at point M) between the plates of the capacitor … can be measured and is seen to be the same as that just outside (at P).”
Displacement Current – “In some cases, for example, steady electric fields in a conducting wire, the displacement current may be zero since the electric field E does not change with time.”