Final answer:
Devices for nominal 120-volt circuits are typically marked 120V. For string lights, older series wired sets will go out if one bulb fails, whereas newer short-circuiting bulb sets continue to function with a slightly higher voltage per remaining bulb. Power is transported at high voltages to minimize losses, and a 120V device, if connected to 240V, will see a fourfold increase in power consumption.
Step-by-step explanation:
Devices meant for use on nominal 120-volt circuits are typically marked 120V. This implies that the devices are intended to operate on circuits where the voltage is approximately 120 volts, though the actual voltage can vary slightly due to fluctuations in the power supply or other factors.
In the context of the holiday lights operation, if a bulb in an older series wired configuration burns out and thus functions like an open switch, the electrical path is broken and the remaining bulbs will not light up. If the string has 40 identical bulbs connected to a nominal 120V power source, each bulb would normally operate at 120V / 40 bulbs = 3V per bulb. Conversely, in the newer versions with short-circuiting bulbs, if one bulb burns out, it will bypass itself and the remaining bulbs will still light up. With one bulb out, the remaining 39 bulbs would have an increased operating voltage of 120V / 39 bulbs, yielding approximately 3.08V per bulb.
Regarding the power transport question, power companies use high voltages for long-distance transmission despite the minor losses due to heating in transformers, as transporting at high voltage and lower current reduces the overall power loss across power lines.
When comparing two devices with the same power consumption but designed for different voltages (120V AC and 240V AC), assuming the power (P) of the devices is the same and using the formula P = V^2 / R, the one designed for 240V AC will have a resistance that is four times as high as the 120V AC device because power is proportional to the square of the voltage when resistance is constant. The current (I), however, which is given by I = P / V, will be half as much for the 240V AC device as compared to the 120V AC device.
If a device intended for 120V AC operation is connected to 240V AC and assuming resistance doesn't change, the power will increase by a factor of four, as power is proportional to the square of the voltage increase.