In a series circuit, the total resistance is the sum of the individual resistances. Which option best describes this?

• A. The total resistance is the product of the individual resistances.
• B. The total resistance is the sum of the individual resistances.
• C. The total resistance is the difference of the resistances.
• D. The total resistance is the quotient of the resistances.

Answer: (B)

In a series circuit, the same current flows through every resistor, so the voltage drops add up. Using V = IR, the voltage across each resistor is I times its resistance, and the total voltage is the sum of those drops: V_total = I(R1 + R2 + ...). Since V_total also equals I times the total resistance, the total resistance must be R1 + R2 + ... . For example, 2 ohms and 3 ohms in series give 5 ohms total. The other formulations—multiplying, subtracting, or dividing the resistances—don’t reflect how voltages add in series, so they don’t describe the total resistance correctly.