Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingEasy
A client has a 240V resistive heating element with a current draw of 20A. What is the resistance of the heating element?
- A4800 Ω
- B0.083 Ω
- C12 Ω
- D24 Ω
Show answer & explanationAnswer & explanation
Correct answer: C. 12 Ω
Using Ohm's Law, Resistance (R) = Voltage (V) / Current (I). So, R = 240V / 20A = 12 Ω.
Why the other options are wrong
- A. This is a calculation of Power (P = V * I) instead of resistance.
- B. This is a calculation of current if resistance were 240V and voltage 20A, or an inverse calculation (I/V).
- D. This might result from incorrectly dividing voltage by half the current or similar error.
Ohm's Law for Resistance
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them. For resistance, it's V/I.
- R = V / I
- Units: Volts (V), Amperes (A), Ohms (Ω)
- Fundamental to DC and AC circuit analysis
Memory trick: VIR: Voltage Is Resistance times Current. For Resistance, cover R and you get V over I.