If three resistors of 10.0 ohms each are placed in series, the total resistance is?

• A. 10.0 ohms
• B. 30.0 ohms
• C. 40.0 ohms
• D. 20.0 ohms

Answer: (B)

In a series circuit, the total resistance is the sum of all resistors. Each resistor adds to the opposition to current, and the same current flows through every element, so their resistances simply add up.

Here you have three resistors, each 10 ohms, lined up in series. Add them: 10 + 10 + 10 = 30 ohms. So the total resistance is 30.0 ohms.

The other numbers would come from counting fewer resistors (one resistor gives 10.0 ohms, two in series give 20.0 ohms) or mixing up a parallel arrangement, which yields a different total than the simple sum.