A specialized ammeter used to measure the current flow between the anode and cathode in the external circuit has what type of resistance?

• A. Zero Resistance
• B. Infinite Resistance
• C. Moderate Resistance
• D. Variable Resistance

Answer: (A)

To measure the current between the anode and cathode without altering the circuit, the measuring instrument must present essentially no resistance. An ammeter with near-zero resistance acts like a short circuit, so it adds almost no voltage drop to the external circuit and the full current can flow through it. In corrosion testing, this lets you capture the true short-circuit current that drives the electrochemical reactions at the electrodes, which is what you want to quantify for corrosion rates. If the ammeter had any significant resistance, it would drop voltage, reduce the current, and give an inaccurate reading. Infinite resistance would stop the current entirely, while moderate or variable resistance would change the current unpredictably and distort the measurement. So the specialized ammeter is described as having zero (nearly zero) resistance.