CBSE - XII Science - Physics - Moving Charges and Magnetism
GIVE THE DETAILED DESCRIPTION ABOUT TANGENT GALVANOMETER
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- 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 is the device which was used to measure small amounts of electric current.
- 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.
- 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.
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