The instrument used to measure electric current is an ammeter.

An ammeter is an instrument used to measure the flow of electric current in a circuit. It is an essential tool in electrical engineering and is commonly used in various applications, including industrial, commercial, and domestic settings. The ammeter provides an accurate measurement of the current passing through a specific point in an electrical circuit.

Working Principle:
The working principle of an ammeter is based on the concept of the electromagnetic effect. It consists of a coil of wire that is placed in the path of the electric current to be measured. When current flows through the coil, it creates a magnetic field around it. The strength of this magnetic field is directly proportional to the amount of current passing through the coil.

Key Components:
- Coil: The coil is the primary component of an ammeter, consisting of a large number of turns of wire wound around a cylindrical or rectangular frame. The wire used is usually made of a material with low resistance, such as copper or aluminum.
- Scale: The ammeter also features a scale that displays the measured current in suitable units, such as amperes (A) or milliamperes (mA).
- Pointer: The ammeter has a pointer attached to the coil, which moves along the scale to indicate the measured current. The pointer is usually a small magnetic needle or a thin metal strip.

Usage and Limitations:
Ammeters are used in various electrical systems and devices to monitor and control the flow of current. They can be used to measure both direct current (DC) and alternating current (AC). However, it is important to note that ammeters have a limited range of current they can measure. If the current exceeds this range, it can damage the instrument or provide inaccurate readings.

Conclusion:
In conclusion, an ammeter is the instrument used to measure electric current accurately. It works based on the principle of the electromagnetic effect and consists of a coil, scale, and pointer. Ammeters are widely used in electrical engineering and play a crucial role in monitoring and controlling current flow in various applications.