Why do lights dim when a large appliance is switched on$?$ The answer is that the large current the appliance motor draws causes a significant potential drop in the wires and reduces the voltage across the lights. This is called an IR drop because it is simply due to the current and resistance of the device in question. Assume the bulb in question dissipates P$2=75$ W when connected to the $120$ V AC source. What average power will the bulb dissipate if I$1=15$ A passes through the wires when the motor comes on$?$ Assume a negligible change in bulb resistance, while the resistance of the wires are R$1=0\mathrm{.}65.$