Images(4)

tangent galvanometer

Datecirca 1860

Inventory Number0204a

ClassificationGalvanometer

Subject

Attributed to Thomas Hall fl. 1840 - 1875

Cultural Region

Place of Origin

Dimensions52 × 54 × 31 cm (20 1/2 × 21 1/4 × 12 3/16 in.)

Material

DescriptionCoil wound on a large cast iron ring (painted red), which is supported on a wooden base (painted green with gold stripes). There is a platform in the center of the coil on which a magnetic compass or electromagnet would be placed. There are brass binding posts.

Signedunsigned

FunctionA tangent galvanometer measures the strength of an electric current. It has a circular coil with a turn of wire and a magnetic needle at the center that is either balanced on a point or suspended by a fiber of silk or quartz. The meter has to be first aligned in the north-south direction and thus the instrument takes into account the earth's magnetic field. When a current is sent through the coil, the needle is deflected according to the vector sum of the field produced by the earth and by the unknown current in the coil. The tangent of the needle's angle of deflection is proportional to the strength of the unknown current producing it.

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