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Physics · 2026 · 3 marks
CBSE 2026 · Region 5 · Set 3 · Q22
What is meant by displacement current? A capacitor is being charged by a battery. Show that Ampere-Maxwell law justifies continuity and constancy of…
What is meant by displacement current ? A capacitor is being charged by a battery. Show that Ampere-Maxwell law justifies continuity and constancy of the current flowing in the circuit.
Marking-scheme solution
Displacement current: the current due to a varying electric field between the plates of a capacitor.
Ampere–Maxwell law: ∮ B⃗·dl⃗ = μ₀ (I_c + I_d).
Outside the capacitor, I_d = $\displaystyle 0$, so I = I_c.
Inside the capacitor, I_c = $\displaystyle 0$, so
I = I_d = ε₀ dΦ_E/dt = ε₀ (d/dt)(Q/ε₀) = dQ/dt = I_c.
Hence I_c + I_d has the same value at all points, i.e. the current is continuous and constant through the circuit.
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CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.