In a series circuit, how is the total resistance Rs computed?

• A. Rs = 1/(1/R1 + 1/R2 + 1/R3)
• B. Rs = R1 + R2 + R3
• C. Rs = V / I
• D. Rs = R1 * R2 * R3

Answer: (B)

In a series circuit, the same current flows through every component, and the total voltage is the sum of the voltage drops across each resistor. Using Ohm’s law for each resistor gives V1 = I R1, V2 = I R2, V3 = I R3. The total voltage is V = V1 + V2 + V3 = I(R1 + R2 + R3). Since the total resistance relates voltage and current by V = I Rs, the total resistance is Rs = V/I = R1 + R2 + R3. So the total resistance in a series circuit is simply the sum of the individual resistances. The other expressions describe different situations (like parallel combinations or the overall V/I ratio) and don’t directly express Rs in terms of R1, R2, and R3 for a series setup.