An ammeter has a typical impedance of less than ____ ohm(s).

• A. 1
• B. 0.1
• C. 0.01
• D. 0.001

Answer: (B)

To measure current without disturbing the circuit, an ammeter must present very little resistance. A low impedance minimizes the burden voltage (voltage drop across the meter) and keeps the circuit current from changing due to the meter itself. Because of this, ammeters are designed with very small resistance, typically described as less than 0.1 ohm. Values like 1 ohm would cause a noticeable voltage drop and alter the current, while 0.01 or 0.001 ohm are much smaller and used only in specialized high-current applications. So, saying the typical impedance is under 0.1 ohm best reflects how these meters are usually built.