If you want to calculate ac or dc resistance like a genuine electrical engineer follow this post. You have to know the current type, power value, voltage, and power factor.

#### Voltage

**Voltage**, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points. The difference in electric potential between two points (i.e., voltage) in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points.

In the International System of Units, the derived unit for voltage is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge).

The official SI definition for volt uses power and current, where 1 volt = 1 watt (of power) per 1 ampere (of current). This definition is equivalent to the more commonly used ‘joules per coulomb’. Voltage or electric potential difference is denoted symbolically by ∆V, but more often simply as V, for instance in the context of Ohm’s or Kirchhoff’s circuit laws.

#### Power

Electric **power**, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter P. The term wattage is used colloquially to mean “electric power in watts.” The electric power in watts produced by an electric current I passing through an electric potential (voltage) difference of V is:

where

- P is electric power in watts
- cos φ is the power factor
- I is the electric current in amperes
- U is electric potential or voltage in volts

#### Power factor

The **power factor** of an AC electrical power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit

The power factor is defined as the ratio of real power to apparent power. As power is transferred along a transmission line, it does not consist purely of real power that can do work once transferred to the load, but rather consists of a combination of real and reactive power, called apparent power. The power factor describes the amount of real power transmitted along a transmission line relative to the total apparent power flowing in the line.

#### Electrical resistance

*Resistance* is a measure of the opposition to current flow in an electrical circuit. *Resistance* is measured in ohms, symbolized by the Greek letter omega (Ω).

The higher the resistance in ohms, the more opposition a substance offers to the movement of electrons. For wires, the resistance is sometimes specified in terms of ohms per unit length (foot, meter, kilometer, or mile). In an electrical system, engineers strive to minimize the resistance (or ohmic value ) because resistance converts electricity into heat, reducing the efficiency that the engineers want and increasing the loss that they don’t want.

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