In the circuit shown in figure, switch S1 is initially closed and S2 is open. Find Va–Vb
Switch S2 is open so capacitor is not in circuit.
Current through 3 Ω registor =243+3=4 A
Let potential of point 'O' shown in fig. is Vo
then using ohm's law
Vo−Va=3× 4=12V ....(i)
Now current through 5Ω resistor =245+1=4A
So Vo−Vb=4× 1=4V ....(ii)
From equation (i) and (ii) Vb−Va=12-4=8V.