In a circuit with three 3-ohm resistors in series, what is the equivalent resistance?

• A. 12 ohms
• B. 9 ohms
• C. 3 ohms
• D. 6 ohms

Answer: (B)

In a series circuit, the total resistance is simply the sum of the individual resistances because the same current flows through each resistor. With three resistors at 3 ohms each, the total is 3 + 3 + 3 = 9 ohms. The other numbers don’t fit: 12 ohms would require four 3-ohm resistors, 3 ohms would be just one resistor, and 6 ohms would come from only two in series. So the equivalent resistance is 9 ohms.