Physics

The key is to find each bulb's resistance first using the power rating, then apply series and parallel rules. A bulb marked "60 W, 220 V" tells you its resistance when operating at that voltage—use $P = \frac{V^2}{R}$ to find $R$. Once you have both resistances, series means they add (same current, voltages split), while parallel means reciprocals add (same voltage, currents split). The mains voltage stays 220 V in both cases; you're just finding what total current the supply must provide.

The key is to find each bulb's resistance first using the power rating, then apply series and parallel rules. A bulb marked "60 W, 220 V" tells you its resistance when operating at that voltage—use $P = \frac{V^2}{R}$ to find $R$. Once you have both resistances, series means they add (same current, voltages split), while parallel means reciprocals add (same voltage, currents split). The mains voltage stays 220 V in both cases; you're just finding what total current the supply must provide.