Electrical Exam · Free practical tool

Ohms law calculator

Choose the two quantities actually given in a resistive circuit question. Show the rearrangement rather than guessing from a formula triangle.

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The method

V = IR; P = VI = I²R = V²/R. Use only the selected pair of known values.

Before using the result

  • Positive DC or purely resistive steady-state values. Unselected inputs are ignored; AC reactive loads require the AC power calculator.

Worked examples

These original training examples illustrate the method for Journeyman Electrician Core Knowledge Review (JE). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.

1. Worked example

Choose the two quantities actually given in a resistive circuit question. Show the rearrangement rather than guessing from a formula triangle.

Known values
Voltage and resistance
Voltage (V)
230
Resistance (Ω)
23
  1. Known pair: Voltage and resistance. Other input values are ignored.
  2. V = I × R = 10 × 23 = 230 V.
  3. P = V × I = 230 × 10 = 2300 W.
  • Voltage: 230 V
  • Current: 10 A
  • Resistance: 23 Ω
  • Power: 2,300 W

2. Comparison example

Compare a different supplied condition using the same method. For Electrical Exam, the important check is that the input meaning, units and method assumptions still match the problem.

Known values
Voltage and resistance
Voltage (V)
120
Resistance (Ω)
23
  1. Known pair: Voltage and resistance. Other input values are ignored.
  2. V = I × R = 5.217391304347826 × 23 = 120 V.
  3. P = V × I = 120 × 5.217391304347826 = 626.0869565217391 W.
  • Voltage: 120 V
  • Current: 5.217391 A
  • Resistance: 23 Ω
  • Power: 626.087 W

Check your understanding

1. Which relationship is used?

V = IR; P = VI = I²R = V²/R. Use only the selected pair of known values.

2. Which assumption should you check first?

Positive DC or purely resistive steady-state values. Unselected inputs are ignored; AC reactive loads require the AC power calculator.

3. How should you verify a different unit system?

Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.

Continue with the matching exam topic

This tool connects to Journeyman Electrician Core Knowledge Review (JE) free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.

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