Why Current Is Continuous Inside the Capacitor Gap
Physics · Electromagnetic Waves · NEET
No real charge crosses the gap between capacitor plates, yet the current does not "stop" there. The changing electric field in the gap creates a displacement current that exactly equals the conduction current in the wires, so the total current is continuous everywhere in the circuit. Memory hook: "Wire current in, field current across" — the gap carries the same current, just in a different form.
In a charging capacitor, no charge crosses the gap, but the changing electric field creates a displacement current id equal in size and direction to the wire current I, keeping the current continuous everywhere.
Your doubts, answered
Do electrons actually jump across the gap between the plates?
No. No real charge crosses the empty gap. Electrons pile up on one plate and leave the other plate, so conduction current flows only in the wires. Inside the gap the electric field grows with time, and this changing field acts like a current (displacement current). So charge never crosses, but the current stays continuous.
Is the displacement current in the gap equal to the wire (conduction) current?
Yes, always. While the capacitor charges, the displacement current id in the gap exactly equals the conduction current I in the wires. This is why the current is continuous: id = I = C(dV/dt). If they were unequal, current would 'break' at the plates, which cannot happen.
Does the displacement current flow in the same direction as the wire current?
Yes. The displacement current points in the same direction as the conduction current and has the same size, so it neatly continues the current through the gap. NEET 2024 tested exactly this: magnitude equal to I, same direction.
What is 'continuity of current' in simple words?
It means the current does not suddenly appear or vanish anywhere in a closed circuit. Whatever current enters one plate as conduction current must continue across the gap as displacement current and come out the other side. Maxwell added displacement current so this rule holds even inside a capacitor.
If the gap is vacuum or air, how can there be any current there?
Even in vacuum, a changing electric field E creates a displacement current id = e0(dPhiE/dt). No matter or charge is needed; only a time-varying field. That is why the current is continuous even across an empty gap.
⚠️ The NEET trap ✗ There is no current inside the gap because charge cannot cross the empty space, so the circuit current stops at the plates. ✓ The current is continuous: the changing field in the gap gives a displacement current equal in size and direction to the conduction current in the wires, id = I = C(dV/dt). 🧠 NTA loves the word 'gap' to make you say 'zero'. Remember: no charge crosses, but current still continues as displacement current.
Real NEET questions
NEET 2019
A parallel plate capacitor of capacitance 20 uF is being charged by a voltage source whose potential is changing at the rate of 3 V/s. The conduction current through the connecting wires and the displacement current through the plates of the capacitor would be, respectively,
A · Zero, 60 uA
B · 60 uA, 60 uA ✓
C · 60 uA, zero
D · Zero, zero
Solution: Conduction current in the wires: I = C(dV/dt). Step 1: put values, C = 20 uF = 20 x 10^-6 F, dV/dt = 3 V/s. Step 2: I = (20 x 10^-6)(3) = 60 x 10^-6 A = 60 uA. Step 3: For current to be continuous, the displacement current in the gap must equal the conduction current, id = I = 60 uA. So both are 60 uA. Answer B.
NEET 2024
A parallel plate capacitor is charged by connecting it to a battery through a resistor. If I is the current in the circuit, then in the gap between the plates,
A · Displacement current of magnitude equal to I flows in the same direction as I ✓
B · Displacement current of magnitude equal to I flows in a direction opposite to that of I
C · Displacement current of magnitude greater than I flows but can be in any direction
D · There is no current
Solution: Step 1: While charging, conduction current I flows in the wires but no charge crosses the gap. Step 2: To keep the current continuous, the changing electric field in the gap produces a displacement current id. Step 3: Maxwell's condition gives id = I in magnitude and in the same direction, so the current continues smoothly across the gap. Answer A.
Solved Electromagnetic Waves NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. The conduction current in the wires continues across the gap as a displacement current of equal size and direction, so the current is continuous everywhere in the circuit.
What carries the current inside the gap?
A time-varying electric field. As the capacitor charges, E in the gap increases, and this changing field acts as a displacement current id = e0(dPhiE/dt). No real charge crosses the gap.
Is displacement current equal to conduction current?
Yes, while charging. id = I = C(dV/dt) at every instant, which is exactly why the current does not break at the plates.
Why did Maxwell introduce displacement current?
Ampere's law failed for a charging capacitor because the current seemed to stop at the plates. Maxwell added the displacement current so that the total current is continuous and Ampere's law works for every surface.
Does any charge move across the plates?
No. Charge only builds up on the plates; none crosses the empty gap. The continuity is maintained by the changing electric field, not by moving charge.
