A short of resistance 0.100 ohm forms across a 120-V supply. What thermal power does it dissipate?

1. Voltage and resistance are known, so use P = V squared / r. 2. Square the voltage: (120 V) squared = 14400 V squared. 3. Divide by the resistance of the short: P = 14400 V squared / 0.100 ohm. 4. That gives P = 144000 W, or 144 kW. 5. This is far larger than any household appliance, which is why a short melts or ignites what surrounds it. 6. 14.4 kW is the trap of dividing by 1.00 ohm instead of 0.100 ohm. 7. 1.20 kW would follow from using P = V I with the resistance mistaken for a current in amperes. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Thermal Hazards_