Final answer:
A short circuit is an undesired low-resistance path between terminals of a voltage source, which can cause excessive power dissipation leading to melting of materials or ignition.
Step-by-step explanation:
A short circuit, also known as a "short," is a condition in which there is an undesired low-resistance path between the terminals of a voltage source. This situation occurs when insulation on wires is compromised, such as when it has worn through, allowing two wires to come into contact with a very low resistance "r." This is very dangerous because it leads to a high power dissipation, calculated with the formula P = V²/r, where P is the power, V is the voltage, and r is the resistance. For example, with a voltage of 120 V and a resistance of 0.100 Ω (ohms), the power would be 144 kW, which is far greater than what a typical household appliance uses. This excessive power can quickly cause materials to melt or ignite due to the rapid increase in temperature.
For example, if the voltage is 120V and the resistance is 0.100Ω, the power dissipated would be 144kW. The rapid dissipation of thermal energy in a short circuit can cause the surrounding materials to melt or ignite.