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Physics · 2026 · 3 marks
CBSE 2026 · Region 5 · Set 2 · Q27
Differentiate between conduction current and displacement current. A capacitor is connected across a source providing time-dependent current. Explain…
Differentiate between conduction current and displacement current. A capacitor is connected across a source providing time-dependent current. Explain how the total current at an instant is the sum of conduction current and displacement current in the circuit at that instant.
Marking-scheme solution
| Conduction current | Displacement current |
| Current in a conductor due to the flow of charge carriers, $\displaystyle I_{c}=\dfrac{d Q}{d t}$ | Current due to a time-varying electric field and hence electric flux in a region, $\displaystyle I_{D}=\varepsilon_{0} \dfrac{d \phi_{e}}{d t}$ |
Maxwell corrected Ampere's circuital law: the source of a magnetic field is not just the conduction current due to the flow of charges, but also the time rate of change of the electric field.
Therefore $\displaystyle I=I_{C}+I_{D}$
$\displaystyle I=\dfrac{d Q}{d t}+\varepsilon_{0} \dfrac{d \phi_{e}}{d t}$
Outside the capacitor plates, only conduction current flows: $\displaystyle I_{D}=0, \ I=I_{C}$
While inside the capacitor: $\displaystyle I_{D}=I, \ I_{C}=0$
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