Electric measurement. Electric current is the movement of electric charges. A common form of current is the movement of electrons through a metal wire. This movement produces several observable effects, including heat and magnetism. A changing current in one wire can induce (cause) a current in a nearby wire. This effect is called inductance. We can use these effects to measure electricity.
Electric current is measured in amperes. An instrument called an ammeter is used to measure electric current. The quantity of electricity carried by an electric current, also known as electric charge, is measured in coulombs. An ampere is a current of 1 coulomb per second.
Electric current results from a difference in electric potential (potential energy per unit charge). This difference causes an electric charge to move from one point to another. Electric potential is measured in volts. A volt is defined as the difference in electric potential between two points on a wire that is carrying 1 ampere of current and producing 1 watt of power. A watt is a unit of electric power measured in joules (a unit of energy) per second. It is measured by a wattmeter. A volt can also be defined as the potential difference between two points that will produce 1 joule of energy for every coulomb of charge that passes between the two points.
The opposition of a material to electric current is called resistance. Electric resistance is equal to the difference in electric potential divided by the electric current. It is measured in ohms. An ohm is the resistance of a conductor carrying 1 ampere of current when the potential difference across the conductor is 1 volt. An instrument called an ohmmeter is used to measure resistance.
