Electric power calculations voltage current and resistance - electricity calculation - electrical power formula ohms law formula wheel power formulas amps watts volts ohms cosine equation

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• Formulas and calculations •

Electricity and Electric Charge

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 or international ampere, R = resistance.
V = voltage, electric potential difference or E = electro motive force (EMF = voltage).

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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 (electric) 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 (mechanic) 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.
Undistorted powerful sound is not to find in these formulas. Please, mind your ears!
The eardrums are really only moved by the sound pressure. That does not do the
intensity, the power or the energy.
Electric (electrical) Energy is E = P × t - measured in watthours, or also in kWh.

Very loud sounding speakers should have much power, but look closer at the very
important efficiency of loudspeakers.

Tip: The electrical power triangle (power formula)

The magic triangle can be used to calculate all formulas of the "electric power law". You hide with
a finger the value to be calculated. The other two values show then how to do the calculation.

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

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ALTERNATING CURRENT (AC) ~

V_l = line voltage (volts), V_p = phase voltage (volts), I_l = line current (amps), I_p = phase current (amps)
Z = impedance (ohms), P = power (watts), φ = power factor angle, VAR = volt-amperes (reactive)

Current (single phase): I = P / V_p×cos φ	Current (3 phases): I = P / √3 V_l×cos φ or I = P / 3 V_p×cos φ
Power (single phase): P = V_p×I_p×cos φ	Power (3 phases): P = √3 V_l×I_l×cos φ or P = √3 V_p×I_p×cos φ

Power factor PF = cos φ = R/(R2 + X2)^1/2, φ = power factor angle. For the purely resistive circuit, PF = 1 (perfect).

Conversions of more different units

In acoustics we got "Ohm's law as acoustic equivalent"

Relationships of acoustic quantities associated with plane progressive acoustic sound waves

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voltage or volt E or V =		volts V
amperage or current I =		amperes, amps A
resistivity or resistance R =		ohms Ω
wattage or power P =		watts W

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