# Electrical Power

JoVE Core
Physik
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JoVE Core Physik
Electrical Power

### Nächstes Video26.9: Electrical Energy

The product of the current flowing through a conductor and the voltage across it is known as electric power. The SI unit of electric power is the watt.

Consider a potential difference across a conductor. The electrical field in a conductor is directed from higher to lower potentials. Since the change in the potential difference is negative, the electric field can be determined.

If the charge is positive, the electrical field exerts a force on the charge and moves it through the conductor.

The work done on the charge is equal to the product of the electric force and the length at which the force is applied.

The power dissipated by the material in the form of heat and light is equal to the time rate of change of the work.

In a circuit with a resistor, the potential drop across the resistor is dissipated as heat. By recalling Ohm's law, the power dissipated by the resistor can be calculated.

A relationship can be established between power, current, voltage, and resistance for all ohmic devices.

## Electrical Power

Electric power is the product of current and voltage, represented in units of joules per second, or watts. For example, cars often have one or more auxiliary power outlets with which you can charge a cell phone or other electronic devices. These outlets may be rated at 20 amps and 12 volts, so that the circuit can deliver a maximum power of 240 watts. Consider a 25 Watt bulb and a 60 Watt bulb. The conversion of electrical energy produces heat and light, while the kinetic energy lost by the electrons in collisions is converted into the internal energy of the conductor and radiation. Therefore, the 60 Watt bulb glows brighter and warmer than the 25 Watt bulb.

A fuse is a device that protects a circuit from a sudden surge in electric power. It is essentially a short piece of wire between two contacts. During a fluctuation in electricity or power, the kinetic energy of the charge carriers—current—running through a conductor is converted into thermal energy in the conductor. The piece of wire in the fuse is under tension and has a low melting point, designed to heat up and break at the rated current. Fuses act quickly, but there is a small time delay while the wire heats up and breaks. Once the fuse is destroyed, it must be replaced as it protects the rest of the circuit from high power. Similarly, circuit breakers are also rated for a maximum current and remain open to protect the circuit, but can be reset.