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Asked in GSEB Board July 2016 · Dielectric slab
Given: the capacitor is charged and then isolated (disconnected from the battery); a slab of dielectric constant K is inserted.
Idea: an isolated capacitor has nowhere to send or receive charge, so the charge Q on its plates cannot change.
The slab raises the capacitance: C → KC.
Then V = Q/(KC) drops to V/K, and U = (Q²)/(2KC) drops to U/K.
So the quantity that remains constant is the charge Q.
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