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What is the rule for finding the equivalent resistance of several resistors connected in series?
AAdd the individual resistances together
BAdd the reciprocals, then take the reciprocal of the sum
CMultiply the individual resistances together
DTake the average of the individual resistances
Answer & Solution
Correct answer: A. Add the individual resistances together
1. In a series circuit, the same current flows through every resistor.
2. The battery voltage equals the sum of the individual voltage drops, V1 + V2 + V3, each equal to I times that resistor's resistance.
3. Factoring out the common current shows the equivalent resistance is the sum R1 + R2 + R3.
4. Averaging or multiplying the resistances does not follow from this derivation, so those options are incorrect.
_Source: OpenStax Physics (CC BY 4.0), Ch 19 "Electrical Circuits", section Resistors in Series and Equivalent Resistance_
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