An ammeter is a very low impedance device and must be connected in series with the load to measure current.

• A. Ammeter
• B. Ohmmeter
• C. Voltmeter
• D. Wattmeter

Answer: (A)

An ammeter measures current by having the same current flow through it as through the load, so it must be placed in series with the circuit. Its internal resistance is kept very low to minimize any voltage drop and not disturb the circuit’s operation. When connected in series, the current that passes through the load also passes through the meter, giving an accurate reading of the current.

If you tried to connect it in parallel, its very low resistance would create a near-short across the supply, drawing a large amount of current and drastically altering the circuit—precisely why ammeters are designed for series use.

Ohmmeters measure resistance by injecting a small current from an internal source and reading the result; they are intended to be connected across the component being tested, not in series in a live circuit. Voltmeters are designed to measure voltage and have very high input impedance, so they are connected in parallel with the element to minimize current draw. Wattmeters measure real power and use both a current path and a voltage path, combining measurements from two coils, so their connections reflect both quantities rather than isolating current alone.