Question

in a circuit the current is 0.5amp and a 200 watt lamp is connect as load.what is the voltage of the circuit?​

Answer 1

The correct answer is we don't know. As mentioned in other answers, the actual power being use in this instance is 100 watt, but all we can tell from this is the resistance of the filament while hot. The bulb will have a voltage rating written on it, and a power rating. This bulb could have been a 200 V bulb rated at 100 watt, but it may have been a 100V bulb rated at 50watt which was simply being over voltaged and therefore consuming twice it's rated power.