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The tangent galvanometer is a scientific instrument used to measure electric current, first used in the 19th century. It uses the tangent law of magnetism to measure the strength of magnetic fields. The instrument typically has an upright coil of copper wire with a compass needle in the middle. The needle rotates in response to the magnetic field of the current, and the angle of rotation is measured using a scale and pointer. Some modern versions use beams of light to make small changes in position apparent during experiments.
Electric current is often measured using an instrument called a tangent galvanometer. Able to measure the presence, direction and strength of currents, the instrument was first used in the early 19th century. It typically has an upright coil of copper wire, wound around a circular frame, and a sleeve in the middle. The compass needle generally responds to the magnetic field of the electric current, which in the experiment is compared to the magnetic field of the earth. This scientific instrument has been built in many forms and the more modern ones often use beams of light to determine measurements, while some versions are used to measure the earth’s magnetic field
The instrument works according to the tangent law of magnetism. This principle defines the tangent of the angle, traveled by the compass needle, as proportional to the ratio of how strong are two magnetic fields. These fields are usually perpendicular to each other. The measured currents are typically proportional to the tangent of the same angle through which the needle passes.
A tangent galvanometer is usually placed on a flat surface and the compass is used to align the coil north to south. The compass needle is then typically aligned with the direction of the coil so that when current is applied, the angle of rotation of the needle can be measured. On a tangent galvanometer, the compass needle can rotate in any horizontal direction. A scale on the device has four quadrants, each equal to a quarter of a circle, while a pointer attached to the right-angled needle can provide a means of reading the scale and taking measurements.
Most tangent galvanometers have a single ring, but some types have two rings side by side. The distance between the rings can vary depending on the instrument. For an optimal magnetic field, however, the distance between them should equal the radius of the coil.
A design problem with the tangent galvanometer has often been the need for a short needle that does not dampen the earth’s magnetic field. Small changes in current are often difficult to read if the needle is too short, so some modern types of tangent galvanometer may use a hollow one attached to a mirror. When light is aimed at the mirror, it can pass through the needle and shine onto the scale to make small changes in position apparent during a tangent galvanometer experiment.
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