What device is used to measure electric current when connected in series in a circuit?

The device used to measure electric current in a circuit is the ammeter. An ammeter is specifically designed to be connected in series with the circuit it is measuring, allowing the current flowing through the circuit to pass directly through the device. This configuration is crucial because it allows the ammeter to determine the total current without affecting the circuit's operation significantly.

An ammeter typically has very low resistance to minimize its impact on the circuit. When measuring current, it's important that the ammeter does not add much resistance, as this could alter the flow of current it is attempting to measure.

In contrast, other devices such as voltmeters are used to measure voltage and are connected in parallel in a circuit, not in series. Ohmmeters are used to measure resistance and are not connected in real-time circuits, while galvanometers are sensitive devices used primarily to detect and measure small currents rather than to quantify current flows in the same way an ammeter does.