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Physics · 2025 · 3 marks
CBSE 2025 · Region 1 · Set 1 · Q25
(a) A parallel plate capacitor is charged by an ac source. Show that the sum of conduction current ( I_c ) and the displacement current ( I_d ) has…
(a)
A parallel plate capacitor is charged by an ac source. Show that the sum of conduction current $\displaystyle \left(\mathrm{I}_{\mathrm{c}}\right)$ and the displacement current $\displaystyle \left(\mathrm{I}_{\mathrm{d}}\right)$ has the same value at all points of the circuit.
(b)
In case (a) above, is Kirchhoff's first rule (junction rule) valid at each plate of the capacitor? Explain.
Marking-scheme solution
a) Showing that \(\displaystyle \left(\mathrm{I}_{\mathrm{c}}+\mathrm{I}_{\mathrm{d}}\right)\) has the same value.
b) Explanation of Kirchhoff's first rule at each plate of capacitor.
a) ∵ Total current \(\displaystyle \mathrm{I}=\mathrm{I}_{\mathrm{c}}+\mathrm{I}_{\mathrm{d}}\) outside the capacitor
\[\begin{gathered}
\mathrm{I}_{\mathrm{d}}=0 \\
\therefore \mathrm{I}=\mathrm{I}_{\mathrm{c}}
\end{gathered}
\]
Inside the capacitor
\[\mathrm{I}_{\mathrm{c}}=0
\]
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