# The figure shows two capacitors of capacitance c and charged to same potential c connected in two circuits . What will be the charge on the capacitor after a time $t= cr$ from the start

$(a)\;vc/e, vc \\ (b)\;vc,vc \\ (c)\;vc,vc/e \\ (d)\;vc/e,vc/e$

In 1st case the diode is connected in forward bias and so current flows.
If Q is initial charge on the capacitor the charge reduces to Q/e in time $t= CR$
But $Q= VC$
$\therefore\; Q_t$, charge after time $t =\large\frac{Vc}{e}$
In the second case the diode is connected in reversed bias and so no current flows and the charge in the capacitor remains same ie $Q= VC$
Hence a is the correct answer.
answered Jan 30, 2014 by