(a) In the given figure, three identical bulbs P, Q and S are connected to a battery. (i) Compare the brightness of bulbs P and Q with that of bulb S when key K is closed. (ii) Compare the brightness of the bulbs S and Q when the key K is opened. Justify your answer in both cases. OR (b) Two cells of emf $10\text{ V}$ each, two resistors of $20\text{ }\Omega$ and $10\text{ }\Omega$ and a bulb B of $10\text{ }\Omega$ resistance are connected together as shown in the figure. Find the current that flows through the bulb.