Riddle: Which lamp failed?

Question:

In a circuit showing a battery and four lit lamps, one lamp fails and all lamps go out. Which lamp failed?

Answer:

Any lamp could have failed in this scenario.

When all the lamps in a circuit are connected in series, if one lamp fails, the entire circuit is broken and all the other lamps will go out. This is due to the nature of series circuits where components are connected in a single path for the current to flow.

Therefore, pinpointing a specific lamp that failed is impossible as any of the four lamps could have been the faulty one, causing the rest to stop glowing simultaneously.