Master Electrician Exam (NEC)General Electrical KnowledgeMedium
A master electrician is evaluating a circuit with two 10-ohm resistors connected in parallel, which are then connected in series with a 5-ohm resistor. If the total voltage applied to this circuit is 20V, what is the total current flowing through the circuit?
- A1.5 A
- B2.0 A
- C1.0 A
- D2.5 A
Show answer & explanationAnswer & explanation
Correct answer: B. 2.0 A
First, calculate the equivalent resistance of the two 10-ohm resistors in parallel: (10 * 10) / (10 + 10) = 100 / 20 = 5 ohms. Then, add this parallel equivalent to the series 5-ohm resistor: 5 ohms + 5 ohms = 10 ohms total resistance. Finally, use Ohm's Law (I = V/R): I = 20V / 10 ohms = 2.0 A.
Why the other options are wrong
- A. This would be the current if total resistance was approx 13.33 ohms, incorrect calculation.
- C. This would be the current if total resistance was 20 ohms, incorrect parallel calculation.
- D. This would be the current if total resistance was 8 ohms, incorrect parallel calculation.
Series-Parallel Circuit Analysis
Analyzing series-parallel circuits involves systematically reducing combinations of resistors to their equivalent resistances until a single total equivalent resistance is found, then applying Ohm's Law.
- Resistors in series: R_eq = R1 + R2 + ...
- Resistors in parallel: 1/R_eq = 1/R1 + 1/R2 + ... or R_eq = (R1 * R2) / (R1 + R2) for two resistors.
- Ohm's Law (I=V/R) is used to find total current once total resistance is known.
Memory trick: Combine Resistors, Then Ohm Them.