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Electricity

Ohm’s law, resistance and electrical power

Calculate equivalent resistance, electrical power and consumed energy from voltage, current and duration.

Created v1.0

By Thibaut Grzelak, Mechanical Analysis Engineer

Electricity
01Calculation inputsR = U / I ; P = U · I ; E = P · t
UIR
Input identificationU is the terminal voltage, I the circuit current and R the equivalent resistance.
V
A
h
02

Results

SI
Equivalent resistance
—Ω

Ratio between voltage and current.

Electrical power
—W

Active power for DC or resistive quantities.

Consumed energy
—kWh

Energy over the entered duration.

Primary relationR = U / I ; P = U · I ; E = P · t

DC quantities or RMS values in a resistive circuit. Voltage and current are assumed constant during duration t. Power factor and three-phase circuits are not covered.

01Formulas and symbols

Formulas used

RU / IEquivalent resistance
PU · IElectrical power
EP · t / 1000Energy in kWh
02Assumptions and limits

Scope of validity

  • DC quantities or RMS values in a resistive circuit.
  • Voltage and current are assumed constant during duration t.
  • Power factor and three-phase circuits are not covered.
03Validation example

Reference numerical case

  1. U = 230 V, I = 10 A and t = 1 h.
  2. R = 23 Ω.
  3. P = 2,300 W.
  4. E = 2.3 kWh.

Calculation path and sources

Ohm’s law relates voltage, current and resistance; power uses P = UI.

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External technical sources

Ohm’s law and power

Power formulas using U, I and R

The three expressions are equivalent when quantities are coherent.

P = U · I

Known voltage and current.

P = U · I

P = R · I²

Known resistance and current.

P = R · I²

P = U² / R

Known voltage and resistance.

P = U² / R