A circuit contains two identical resistors in series with a battery whose internal…
PHYSICS · Single correct · A Level · Physics · Electricity · Electricity
Problem
A circuit contains two identical 100Ω resistors in series with a battery whose internal resistance is negligible. A real ammeter with internal resistance 1Ω is placed in series to measure the circuit current, and a real voltmeter with internal resistance 10kΩ is connected across the second resistor. Compared with the current that would exist if no meters were present, which statement about the ammeter reading is most accurate?
(a) It is always higher, because the voltmeter provides an additional parallel pathway that reduces the total circuit resistance far more than the ammeter increases it.
(b) It is slightly lower, because current that flows through the voltmeter is diverted from the main branch, so less current passes through the ammeter.
(c) It is always lower, because the added series resistance of the ammeter reduces the current more than the voltmeter’s parallel connection can compensate.
(d) It is essentially unchanged, because the voltmeter draws almost no current and the ammeter resistance is so small that their effects nearly cancel.