Displacement Current

Hint: Use the concept of displacement current in a charging capacitor and apply Ampere-Maxwell law.

Explanation: As the surface charge density on the plates of a parallel plate capacitor increases at a constant rate, there is a changing electric field between the plates, which gives rise to a displacement current. According to Maxwell’s modification of Ampere’s law, this displacement current produces a magnetic field that forms concentric circles around the axis, similar to the magnetic field around a conduction current. The magnetic field is zero outside the plates, because outside the plates the electric field is nearly zero, so no displacement current flows there. Between the plates, the magnetic field is non-zero and increases with radial distance from the axis, reaching its maximum near the edge of the imaginary cylindrical surface connecting the peripheries of the plates.
Hence, option (1) is the correct answer.