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Asked by preethambasilmartis 21st June 2016, 4:26 PM
In order to understand working mechanism of Tangent Galvanometer, the knowledge of Tangent law of Magnetism is essential.

Tangent law of Magnetism :-
• The tangent law of magnetism states that the tangent of the angle of a compass needle which is due to the movement under the influence of magnetic field is directly proportional to the ratio of strengths of two perpendicular magnetic fields.
• In simpler words, the tangent of the angle made by the moving needle under the magnetic field directly indicates the strength of the perpendicular magnetic fields.
Tangent Galvanometer:-

Definition
• Tangent galvanometer is the device which was used to measure small amounts of electric current.

Construction
• The working of tangent galvanometer is based on the principle of tangent law of magnetism.
• It consists of a coil of insulated copper wire wound on a circular non-magnetic frame.
• It is utmost necessary that the coil wound is done in helical arrangement otherwise, the field due to the wire will affect the compass needle, thus inducing an error in the reading.
• This frame is mounted vertically on a horizontal base for support.
• The coil of insulated copper wire is usually rotated on a vertical axis passing through its centre.
• A small sized magnetic compass with a  powerful magnetic needle is made to pivote at the centre of this coil, such that it is free to rotate in a horizontal plane.
• The circular scale is used to read the movement of this magnetic needle which is divided into four quadrants, each ranging from 0° to 90°.
• A pointer is attached to this needle at right angles, usually made up of thin alluminium as alluminium is lighter in mass.
• The usual way of discarding possibilities of parallax is also used i.e placing of a plane mirror below the compass needle.

Working
• The instrument needle starts moving firstly under the influence of Earth's magnetic field.
• Movement continues untill the magnetic field of earth is parallel with the plane of coil.
• Then, on application of an uknown current, a second magnetic field on the axis of the coil which is perpendicular to the Earth's magnetic field is created.
• Hence the compass needle responds to the vector sum of the two fields.
• This deflection angle is equal to the tangent of the ratio of those two fields.
Answered by Expert 29th November 2017, 3:25 PM
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Tags: galvanometer