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Electric Current 

Electricity and Electric Charge

• Formulas and calculations • 

The relationship between 

Electrical voltage V, amperage I, resistivity R, impedance Z, wattage P 

The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R.Ohm's law equation (formula): V = I × R and the power law equation (formula): P = I × V.P = power, I or J = Latin: influare, international ampere, or intensity and R = resistance.V = voltage, electric potential difference or E = electro motive force (EMF = voltage).

Enter any two of the following values and click the calculation button.The missing values will be calculated. Enter only two values.

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Voltage or volts E or V =   volts VAmperage or current I =   amperes, amps A 

 Resistivity or resistance R =   ohms ΩWattage or power P =   watts W

 

For R take impedance Z   

 

Fundamentals: Electric Laws − Formulary − Equations

 Formula wheel ▼  Important formulas

Electrical engineering laws   Electronic engineering laws

V comes from "voltage" and E from "electromotive force". E means also energy, so V is chosen.

The Big Power Formulas        Electrical and mechanical power calculation 

 Formula 1 − Electrical power equation: Power P = I × V = R × I2 = V2 ⁄ R where power P is in watts, voltage V is in volts and current I is in amperes (DC). If there is AC, look also at the power factor PF = cos φ and φ = power factor angle (phase angle) between voltage and amperage. Formula 2 − Mechanical power equation: Power P = E ⁄ t = W ⁄ t where power P is in watts, Energy E is in joules, and time t is in seconds. 1 W = 1 J/s. Power = force multiplied by displacement divided by time P = F · s / t or: Power = force multiplied by speed (velocity) P = F · v. Electrical Energy is E = P × t − measured in watthours, or also in kWh.

 Undistorted powerful sound is not found in these formulas. Please, mind your ears! The eardrum and microphone diaphragms are really only moved by the waves of

the sound pressure. That does not do either the intensity, nor the power or the energy. If you are in the audio recording business, it is wise not to care much about the energy, power and intensity as the cause, care more about the effect of sound pressure and sound pressure level on the ears and the microphones and the corresponding audio voltage. Sound pressure and Sound power – Effect and Cause Very loud sounding speakers will have a lot of power, but look closer at the very important efficiency of loudspeakers. This includes the typical question: How many decibels (dB) are actually twice or three times as loud? There is really no RMS power. The words "RMS power" are not correct. There is a calculation of power which is the multiplication of a RMS voltage and a RMS current. Watts RMS is meaningless. In fact, we use that term as an extreme shorthand for power in watts calculated from measuring the RMS voltage. Please, read here: Why there is no such thing as 'RMS watts' or 'watts RMS' and never has been. Power is the amount of energy that is converted to a unit of time. Expect to pay more when demanding higher power.

 

 The word "power amplifier" is a misnomer. Power is not really  something that can be "amplified". Voltage and current can be  amplified. The term "power amplifier" although technically  incorrect has become understood to mean an amplifier that is  intended to drive a load such as a loudspeaker. 

Tip: The electrical power triangle (power formula) The magic triangle can be used to calculate all formulas of the "electric power law". You hide

witha finger the value to be calculated. The other two values show then how to do the calculation.

Please enter two values, the third value will be calculated.

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Electrical power P:  wattsVoltage V:  volts

Amperage I:  amps

Calculations: Ohm's law - Ohm's magic triangle

Measurement of input impedance and output impedance

ALTERNATING  CURRENT (AC) ~Vl = line voltage (volts), Vp = phase voltage (volts), Il = line current (amps), Ip = phase current (amps)

Z = impedance (ohms), P = power (watts), φ = power factor angle, VAR = volt-amperes (reactive)

Current (single phase): I = P / Vp×cos φ     Current (3 phases): I = P / √3 Vl×cos φ or I = P / 3 Vp×cos φ 

Power (single phase): P = Vp×Ip×cos φ     Power (3 phases): P = √3 Vl×Il×cos φ or P = √3 Vp×Ip×cos φ 

Power factor PF = cos φ = R/(R2 + X2)1/2, φ = power factor angle. For the purely resistive circuit, PF = 1 (perfect).The apparent power S is calculated according to Pythagoras, the active power P and reactive power Q.

S = √(P2 + Q2)  The true power factor and not the conventional 50/60 Hz displacement power

factor

In acoustics we have an "Acoustic equivalent for ohm's law"

Relationships of acoustic quantities associated with plane progressive sound waves

Conversions of many units, like power and energyprefixes | length | area | volume | weight | pressure | temperature | time | energy | power |

density | velocity | acceleration | force

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