When resistors R1, R2, R3 are in series, how is the total resistance computed?

• A. Take the reciprocal of the sum
• B. Add the resistances together
• C. Multiply the resistances
• D. Subtract the smallest from the largest

Answer: (B)

When resistors are in series, you’re passing the same current through each component, and the total voltage is the sum of all the individual voltage drops. Because resistance is defined as V = I·R and the current through each resistor is the same in a series chain, the total opposition to current is simply the sum of the individual resistances. So the total resistance is R_total = R1 + R2 + R3.

For example, if R1 = 2 Ω, R2 = 4 Ω, and R3 = 6 Ω, the total resistance is 12 Ω.

The other patterns don’t fit series behavior. Taking the reciprocal of the sum would relate to a parallel-type combination, multiplying resistances isn’t how series combines resistance, and subtracting the smallest from the largest doesn’t reflect any standard circuit rule.