CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A circuit has three resistors connected in series: R1 = 10 ohms, R2 = 20 ohms, and R3 = 30 ohms. If the total voltage supplied to the circuit is 120 volts, what is the total current flowing through the circuit?
- A12 amps
- B2 amps
- C6 amps
- D0.5 amps
Show answer & explanationAnswer & explanation
Correct answer: B. 2 amps
For series resistors, total resistance (Rt) is the sum of individual resistances: Rt = 10 + 20 + 30 = 60 ohms. Using Ohm's Law (I = V/R), total current I = 120V / 60 ohms = 2 amps.
Why the other options are wrong
- A. This would be the current if the total resistance was 10 ohms, significantly underestimating the resistance.
- C. This would be the current if the total resistance was 20 ohms (e.g., if only R2 was considered or an error in summation).
- D. This would be the current if the total resistance was 240 ohms, which is incorrect.
Series Circuit Current
In a series circuit, the total current is the same through all components and is determined by the total voltage divided by the total equivalent resistance.
- Current is constant throughout a series circuit.
- Total resistance is the sum of individual resistances (Rt = R1 + R2 + ...).
- Ohm's Law (I = V/R) applies to the total circuit.
Memory trick: Series means sum for resistance, same for current.