In a series circuit, how is the source voltage Vs related to the voltages across components?

• A. Vs = V1 - V2 - V3
• B. Is = I1 = I2 = I3
• C. Rs = R1 + R2 + R3
• D. Vs = V1 + V2 + V3

Answer: (D)

In a series circuit, the same current flows through every component, and the source voltage is divided into voltage drops across each component. The voltages across the components add up to the total supply, so the source voltage equals V1 plus V2 plus V3. This follows Kirchhoff's voltage law: the sum of all voltages around the loop is zero, so Vs − V1 − V2 − V3 = 0, which rearranges to Vs = V1 + V2 + V3. The other ideas describe the current being the same or the total resistance, but they don’t directly state how the source voltage relates to the component voltages.