電力

Electrical power is the product of current flowing through a conductor and the voltage across it, measured in watts (joules per second). The formula is P = IV, where I is current and V is voltage. For example, a 20-amp, 12-volt power outlet delivers 240 watts maximum. This relationship applies to all ohmic devices in a circuit.

When current flows through a resistor, the potential drop across it is dissipated as heat and light. The kinetic energy lost by electrons in collisions is converted into internal energy of the conductor and radiation. Using Ohm's law, power dissipated can be calculated as P = I²R or P = V²/R, establishing relationships between power, current, voltage, and resistance.

A 60-watt bulb dissipates more electrical energy per unit time than a 25-watt bulb. The higher power rating means more electrical energy is converted into heat and light. Consequently, the 60-watt bulb produces greater brightness and warmth due to this increased energy conversion rate.

A fuse is a short piece of wire between two contacts designed to protect circuits from sudden power surges. When current exceeds the rated value, kinetic energy of charge carriers converts to thermal energy, heating the wire until it melts and breaks. This stops current flow, protecting the rest of the circuit. Once destroyed, the fuse must be replaced.

When electrical current flows through a conductor, charge carriers lose kinetic energy through collisions. This lost kinetic energy is converted into thermal energy and radiation within the conductor material. The rate of this energy conversion is the electrical power dissipated, which depends on the current, voltage, and resistance of the conductor.

Both fuses and circuit breakers are rated for maximum current and protect circuits from power surges. However, fuses are one-time devices that must be replaced after melting, while circuit breakers can be reset and reused. Circuit breakers remain open to protect the circuit but offer the advantage of reusability without replacement.

The electric field in a conductor is directed from higher to lower potential. When a potential difference exists across a conductor, the electric field exerts a force on positive charges, moving them through the material. The work done on the charge equals the product of electric force and the distance traveled, which determines the power dissipated.