Thursday, April 1, 2010

Current-carrying coil in a MAgnetic Field

A moving- coil meter ( Ammeter) can be used to measure direct current.
The coil is pivoted on a bearing and its rotation is resisted by hair springs which acts as control springs above and below it.
The soft iron cylinder at the center of the coil is fixed and together with the curved poles of the magnet, it produces a radial field.
When current flows through the coil, an electric field is created as a result of the interaction between the two magnetic fields. this produces a pair of turning forces acting on the coil. The turning forces cause the coil to rotate until stopped by an equal and opposing force on the coil by the springs.
The greater the current, the greater the direction shown by the pointer attached to the coil. hence meter has a linear scale.

The sensitivity of the moving-coil meter is increased by having
i. more number of turns in the coil,
ii. stronger magnets
iii. weaker control springs,
iv. a greater number of turns in the coil.


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