# Us standard voltage and current relationship

### Introduction to circuits and Ohm's law (video) | Khan Academy

Introduction to electricity, circuits, current, and resistance. Practice: Calculating resistance. Electric Current Information for All Countries current, Number of phases, Nominal voltage, Type(s) of plug, Number of American Samoa, All, 60, , A,B ,I. Mains electricity is the general-purpose alternating-current (AC) electric power supply. It is the The two principal properties of the electric power supply, voltage and In the US, mains electric power is referred to by several names including may have a different standard voltage or frequency from the surrounding areas.

The mathematical symbol for each quantity is meaningful as well. Most direct-current DC measurements, however, being stable over time, will be symbolized with capital letters.

Coulomb and Electric Charge One foundational unit of electrical measurement, often taught in the beginnings of electronics courses but used infrequently afterwards, is the unit of the coulomb, which is a measure of electric charge proportional to the number of electrons in an imbalanced state. One coulomb of charge is equal to 6,,, electrons. Cast in these terms, current is the rate of electric charge motion through a conductor.

## Mains electricity

As stated before, voltage is the measure of potential energy per unit charge available to motivate electrons from one point to another. Defined in these scientific terms, 1 volt is equal to 1 joule of electric potential energy per divided by 1 coulomb of charge.

Thus, a 9 volt battery releases 9 joules of energy for every coulomb of electrons moved through a circuit. These units and symbols for electrical quantities will become very important to know as we begin to explore the relationships between them in circuits.

Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate: In this algebraic expression, voltage E is equal to current I multiplied by resistance R. Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively: In the above circuit, there is only one source of voltage the battery, on the left and only one source of resistance to current the lamp, on the right.

In this first example, we will calculate the amount of current I in a circuit, given values of voltage E and resistance R: What is the amount of current I in this circuit? In this second example, we will calculate the amount of resistance R in a circuit, given values of voltage E and current I: Larger household electrical equipment and industrial equipment may be permanently wired to the fixed wiring of the building. For example, in North American homes a window-mounted self-contained air conditioner unit would be connected to a wall plug, whereas the central air conditioning for a whole home would be permanently wired.

Larger plug and socket combinations are used for industrial equipment carrying larger currents, higher voltages, or three phase electric power.

These are often constructed with tougher plastics and possess inherent weather-resistant properties needed in some applications. Circuit breakers and fuses are used to detect short circuits between the line and neutral or ground wires or the drawing of more current than the wires are rated to handle overload protection to prevent overheating and possible fire. These protective devices are usually mounted in a central panel—most commonly a distribution board or consumer unit—in a building, but some wiring systems also provide a protection device at the socket or within the plug.

Residual-current devicesalso known as ground-fault circuit interrupters and appliance leakage current interrupters, are used to detect ground faults - flow of current in other than the neutral and line wires like the ground wire or a person. When a ground fault is detected, the device quickly cuts off the circuit. Measuring voltage[ edit ] A distinction should be made between the voltage at the point of supply nominal voltage at the point of interconnection between the electrical utility and the user and the voltage rating of the equipment utilization voltage.

### How to Understand Electricity: Watts, Amps, Volts, and Ohms | Owlcation

This allows for the voltage drop between equipment and supply. Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages.

Power distribution system voltage is nearly sinusoidal in nature. Voltages are expressed as root mean square RMS voltage. Voltage tolerances are for steady-state operation. Momentary heavy loads, or switching operations in the power distribution network, may cause short-term deviations out of the tolerance band and storms and other unusual conditions may cause even larger transient variations.

- Introduction to circuits and Ohm's law
- Basic electrical quantities: current, voltage, power
- How to Understand Electricity: Watts, Amps, Volts, and Ohms

In general, power supplies derived from large networks with many sources are more stable than those supplied to an isolated community with perhaps only a single generator. Choice of voltage[ edit ] Main article: Mains electricity by country The choice of supply voltage is due more to historical reasons than optimization of the electric power distribution system—once a voltage is in use and equipment using this voltage is widespread, changing voltage is a drastic and expensive measure.

Minimum wire size for hand-held or portable equipment is usually restricted by the mechanical strength of the conductors.

National electrical codes prescribe wiring methods intended to minimize the risk of electric shock and fire. Three-phase systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment. Large loads are connected for the higher voltage.

Other three-phase voltages, up to volts, are occasionally used for special-purpose systems such as oil well pumps. In practice, this allows countries to continue to supply the same voltage or Vat least until existing supply transformers are replaced.

### Basic electrical quantities: current, voltage, power (article) | Khan Academy

Equipment with the exception of filament bulbs used in these countries is designed to accept any voltage within the specified range. The boundary between the two regions contains four back-to-back high-voltage direct-current HVDC substations which interconnect the power between the two grid systems; these are Shin ShinanoSakuma DamMinami-Fukumitsuand the Higashi-Shimizu Frequency Converter.

To accommodate the difference, frequency-sensitive appliances marketed in Japan can often be switched between the two frequencies. History of voltage and frequency[ edit ] See also: