Which type of meter is used to measure very low currents, such as those in bridge circuits?

A galvanometer is specifically designed to measure very low currents, often in the milliamp or microamp range, making it highly suitable for use in precise applications such as bridge circuits. In bridge circuits, accurate current measurements are crucial for determining the balance of the circuit, and the sensitivity of a galvanometer allows for the detection of small changes in current that other meters may not be able to discern.

This type of meter operates on the principle of magnetic deflection, where a small current flowing through a coil generates a magnetic field that moves a needle or pointer on a calibrated scale, providing a visual indication of current flow. This high sensitivity and precision are what set a galvanometer apart from other meters, enabling it to fulfill specialized roles in circuits requiring careful measurements. The other options, while useful in their own right, do not match the precision needed for very low current measurements.