Ohm's Law & Power Calculator

The Ohm's Law Formulas

Exam-Relevant Examples

• A 100W radio drawing 10A from a 13.8V supply — verify: P = E × I = 13.8 × 10 = 138W (some loss in the supply itself)
• A 50Ω dummy load with 100W applied: I = √(P/R) = √(100/50) = 1.41A; E = √(P×R) = √(100×50) = 70.7V
• Fuse sizing: always choose a fuse rated at least 20% above the circuit's expected current draw

• Why does the exam use "E" for voltage instead of "V"?
  The FCC uses E (for electromotive force) in the Technician and General question pools — it is the traditional engineering notation. Both E and V mean voltage; the FCC question pool uses E throughout. The calculator above uses E to match exam terminology.
• How many Ohm's Law questions are on the Technician exam?
  Subelement T5 (Electrical Principles) contributes 4 questions to the 35-question Technician exam. Most of those 4 questions involve Ohm's Law, power calculations, or unit conversions (milliamps to amps, kilowatts to watts). If you master E=IR and P=EI you can answer most of them without needing to memorize the derived formulas.