電位と電位差

Electric potential energy is the total energy stored due to a charge's position in an electric field. Electric potential is the electric potential energy per unit charge, making it independent of the test charge itself. While potential energy depends on the charge magnitude, potential does not. Both are scalar quantities measured in joules and volts respectively.

Electric potential difference is the ratio of change in potential energy to the test charge moved between two positions. It equals the work done per unit charge to move a charge from one point to another. Measured in volts (joules per coulomb), potential difference is also called voltage in electronic circuits and is measured using a voltmeter.

Voltage represents energy per unit charge, not total energy. A 12-volt motorcycle battery and a 12-volt car battery have identical potential differences between terminals, but the car battery can move more total charge. Since energy equals voltage multiplied by charge, the car battery stores more total energy despite having the same voltage.

For multiple point charges, electric potential is found by taking the algebraic sum of potentials from individual charges. For continuous charge distributions, the potential is calculated by integrating charge elements over the distance where potential is measured. This superposition principle allows complex charge configurations to be analyzed systematically.

When a positive test charge moves away from a positive static charge, the Coulomb force does positive work on it. This positive work results in a decrease in electric potential energy. The electric potential at that location also decreases as distance from the source charge increases.

Electric potential and potential difference are measured in volts (V), named after Alessandro Volta. One volt equals one joule per coulomb, representing the energy per unit charge. This unit is fundamental in electronics and physics, appearing on voltmeters and battery labels worldwide.

Electric potential difference equals the work done per unit charge to move a test charge between two points. When a positive charge moves in a static electric field, the work done on it represents a change in potential energy. Dividing this work by the test charge magnitude yields the potential difference between those positions.