CSLB C-10 Electrical ContractorElectrical Theory and CalculationsEasy
A series circuit contains three resistors: R1 = 20 ohms, R2 = 30 ohms, and R3 = 50 ohms. If the circuit is connected to a 120V DC source, what is the total resistance of the circuit?
- A30 ohms
- B100 ohms
- C60 ohms
- D10 ohms
Show answer & explanationAnswer & explanation
Correct answer: B. 100 ohms
In a series circuit, the total resistance is simply the sum of all individual resistances. The voltage source is provided but not needed for this calculation.
Why the other options are wrong
- A. This is a calculation error, likely an incorrect sum.
- C. This is a calculation error, possibly omitting one resistor or making a mistake in addition.
- D. This is a calculation error, possibly confusing it with parallel resistance or an average.
Series Circuit Total Resistance
In a series circuit, components are connected end-to-end, forming a single path for current. The total resistance is the sum of the individual resistances.
- Formula: Rt = R1 + R2 + R3 + ...
- Current is the same through all components.
- Voltage drops across each resistor add up to the source voltage.
Memory trick: Series is simply SUMS: sum the resistance, sum the voltage drops.