# When a bulb is rated at 12V does it mean the voltage drop across it or the voltage of the battery it is connected to?

If we had two light bulbs rated at 6W at 12V both in a circuit where the battery supplies 12V and they were connected in series, doesn't this mean that there would only be a 6V drop across each light bulb?

Does this mean that these lightbulbs aren't in their ideal functioning environment of 12V? Or does the rating simply mean the battery voltage which the circuit is connected in which case these lightbulbs are in their ideal functioning environment?

This problem is bothering me because depending on which I consider I find different answers for the current that flows through the circuit. I would really appreciate some clarification. • 6W at 12V means that the bulbs are designed to be operated at 12V and will put out 6W when so operated. As you pointed out, they will not be operating at 12V in your circuit but at 6V. They'll glow much more dimly than their normal brightness (if they glow at all) in the circuit shown. – user93237 Aug 10 '19 at 1:37
• Also, at lower voltages, in addition to being dimmer, the resistance of the bulbs will also be lower, so they will draw more current at 6 V than half the current they draw at 12 V. – Puk Aug 10 '19 at 1:40
• @Puk this is considering a real-life situation right? But if we were to consider theoretical - would I be correct in considering 1 bulb first and finding the current, then halving it for two bulbs? – tunnelingelectron Aug 10 '19 at 1:44
• I'm not sure what you mean by theoretical. If you mean the light bulb always has the same resistance regardless of the voltage applied (or in other words is "perfectly Ohmic"), then yes. This is just far from the truth in a real light bulb. At higher voltages, the filament of the light bulb will reach a higher temperature, increasing its resistance. – Puk Aug 10 '19 at 1:49

## 1 Answer

doesn't this mean that there would only be a 6V drop across each light bulb?

Yes, assuming the bulbs are identical

Does this mean that these lightbulbs aren't in their ideal functioning environment of 12V?

Yes (more or less). The bulbs will, of course, last much longer operating with 6V across than with 12V across. On the other hand, they will produce much less than their rated light (and heat) output at 12V.