Calculations voltage current resistance and electric power - electricity calculation - electrical power formula general ohms law physics formula wheel formulas amps watts volts ohms cosine equation audio engineering pie chart charge audio engineering sound recording calc

• Formulas and calculations •

The relationship between

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

Electricity and Electric Charge

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).

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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.
Power = force times displacement divided by time P = F · s / t or:
Power = force times speed (velocity) P = F · v.
Electric (electrical) Energy is E = P × t − measured in watthours, or also in kWh.

Undistorted powerful sound is not to find in these formulas. Please, mind your ears!
The eardrums are really only moved by the waves of the sound pressure. That does not
do neither the intensity, nor the power or the energy. If you are in the audio recording
business, it is therefore wise not to care much about cause like energy, power and
intensity, care more about sound pressure and voltage.

Very loud sounding speakers should have much 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" show not correct, that there is a
calculation of a power which is the multiplication of a voltage RMS and an amperage RMS.
RMS watts 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 in 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 with
a 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.

Calculations: Ohm's law - Ohm's magic triangle
Measurement of input impedance and output impedance

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).
The apparent power S is calculated according to Pythagoras, the active power P and reactive power Q. S = √(P² + Q²)

In acoustics we got "Acoustic equivalent for ohm's law"

Relationships of acoustic quantities associated with plane progressive sound waves

Conversions of many other units

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