The voltage across all components in a series circuit adds up to the source voltage.

• A. True
• B. False
• C. Not specified
• D. Depends on components

Answer: (A)

In a series circuit, the same current flows through every component, and Kirchhoff's Voltage Law says the sum of all voltage changes around a closed loop is zero. If we treat the source as providing a single voltage rise, then the voltage drops across each component must add up to that rise. Since each component drops V = I R and the current is the same through all of them, the total drop across all components equals I times the total resistance, which is the source voltage in an ideal circuit. Therefore, the voltages across all components do add up to the source voltage. If there’s internal resistance in the source, the sum of the component voltages equals the terminal voltage, which can be less than the source’s emf, but in the ideal case the statement holds true.