Which is correct in reference to electrical resistance?

• A. Two electrical devices will have the same combined resistance if they are connected in series as they will have if connected in parallel.
• B. If one of three bulbs in a parallel lighting circuit is removed, the total resistance of the circuit will become greater.
• C. An electrical device that has a high resistance will use more power than one with a low resistance with the same applied voltage.
• D. The current in a conductor changes with length only.

Answer: (B)

In parallel circuits, the total resistance is lower than any individual branch because the current has multiple paths to take; conductances add. If you remove one branch, you reduce the number of paths for current, so the total conductance decreases and the total resistance increases. That’s exactly what happens when one bulb is taken out of a parallel lighting circuit—the overall resistance becomes greater.

The other statements don’t fit with how resistance behaves. The combined resistance in series and parallel isn't the same; in series you add resistances, while in parallel you combine conductances, so they aren’t equal. A higher resistance at the same voltage actually draws less power (P = V^2/R), not more. And current in a conductor isn’t determined by length alone; it depends on the whole circuit and the applied voltage, with length affecting resistance as part of that relationship.