An ammeter is a device that measures electric current, which is the flow of electricity through a wire or circuit. The name comes from ampere, the unit used to measure electrical current (usually shortened to amp). Just as a thermometer measures temperature or a speedometer measures speed, an ammeter tells you how many amperes of electricity are flowing.

Electricians use ammeters to check if circuits are working properly or to make sure wires aren't carrying dangerously high currents that could overheat and cause fires. In science class, you might use a simple ammeter to measure the current in a battery-powered circuit you've built with bulbs and wires.

An ammeter must be connected differently than a voltmeter, which measures voltage. While a voltmeter connects across a component (like touching both ends of a battery), an ammeter must be placed directly in the path of the current, so all the electricity flows through it. Think of it like putting a sensor in a water pipe to count how much water flows past, rather than just checking the pressure.

Understanding current flow helps engineers design everything from flashlights to electric cars, making the ammeter an essential tool for anyone working with electricity.