In a series circuit, what happens to the total resistance and current if you add another resistor in series?

• A. Total resistance increases; current decreases
• B. Total resistance stays the same; current stays the same
• C. Total resistance decreases; current increases
• D. Total resistance increases; current increases

Answer: (A)

In a series circuit, resistors line up so their resistances simply add together. Each additional resistor in the path increases the total resistance the current must push through. Because the voltage from the power source is fixed, Ohm’s law (I = V / R) applies: as the total resistance R increases, the current I decreases. So adding another resistor in series makes the total resistance go up and the current go down.

Other statements don’t fit because keeping the total resistance the same is incorrect for series connections—the resistances add. Claiming the current increases would contradict I = V / R when V is fixed. And saying both resistance and current increase would violate the same relationship between resistance and current in a fixed-voltage circuit.