The total resistance in a 120 V circuit in series with three 10 Ω resistors is ____.

The total resistance in a 120 V circuit in series with three 10 Ω resistors is ____.

• A. 120 Ω
• B. 30 Ω
• C. 3 Ω
• D. 10 Ω

Answer: (B)

In a series circuit, the total resistance is the sum of all resistors. With three resistors of 10 Ω each in series, you add them up: 10 Ω + 10 Ω + 10 Ω = 30 Ω. The 120 V source helps you find the current once you know the total resistance (I = V/R), which would be 120 V / 30 Ω = 4 A, but the question asks for the total resistance, which is 30 Ω. If you tried to get 120 Ω, or 3 Ω, or 10 Ω, you’d be contradicting the fact that resistors in series add together; in this setup the total cannot exceed 30 Ω or be less than 10 Ω.

In a series circuit, the total resistance is the sum of all resistors. With three resistors of 10 Ω each in series, you add them up: 10 Ω + 10 Ω + 10 Ω = 30 Ω. The 120 V source helps you find the current once you know the total resistance (I = V/R), which would be 120 V / 30 Ω = 4 A, but the question asks for the total resistance, which is 30 Ω. If you tried to get 120 Ω, or 3 Ω, or 10 Ω, you’d be contradicting the fact that resistors in series add together; in this setup the total cannot exceed 30 Ω or be less than 10 Ω.