# Power of Bulbs Connected in Series and Parallel

Let's say that I have a circuit consisting of a power supply of $$220V$$ and $$2$$ bulbs of power-voltage rating $$40W-220V$$ and $$60W-220V$$ in series. How would I calculate the current flowing across the circuit? I know how to calculate it if there is a single bulb (Using $$P = I^2 * R$$, $$P = V^2/R$$ and $$P = VI$$), but I'm confused about the use of the formulae for multiple bulbs/appliances.

• I think there is information missing, what is the voltage rating of bulb ? @Twilight Mar 19, 2021 at 18:12
• Edited it now :) Mar 19, 2021 at 18:22
• @ShreyanshPathak I see. But how do I calculate the resistance in this case? Mar 19, 2021 at 18:22
• @ShreyanshPathak This is an answer. It's improper to post answers as comments. Mar 19, 2021 at 19:44

An incandescent bulb is simply a resistor. The $$P$$-$$V$$ rating of a bulb is a statement about how much power the bulb would consume if placed in parallel with a $$V$$ voltage supply. Assuming the relationship of $$P=\frac{V^2}{R}$$ one can calculate the effective resistance of an individual bulb. The $$P$$ and $$V$$ used here are completely independent of any actual circuit, and are the numbers which tell you the resistance of the bulb.