Question

describe Kelvin method to determine the resistance of galvanometer.

Answer 1

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The Kelvin double bridge is the modification of the Wheatstone bridge and provides greatly increased accuracy in measurement of low value resistance. An understanding of the Kelvin bridge arrangement may be obtained by the study of the difficulties that arise in a Wheatstone bridge on account of the resistance of the leadsand the contact resistances while measuring low valued resistance.The Kelvin double bridge incorporates the idea of a second set of ratio arms-hence the name double bridge-and the use of four terminal resistors for the low resistance armsPRINCIPLE:The principle of wheat stone bridge is used in order to measure the unknown resistance of galvanometer while knowing the three resistances.


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Answer 2

Kelvin's method to determine resistance of a galvanometer is performed using a meter bridge( follows the principle of Wheatstone bridge).

In the setup of the experiment, the galvanometer( the resistance of which is to be found) is connected in the left gap and a resistance box( having a particular resistance) in the right gap of a meter bridge.

The rest of the requirements like emf cell, key, rheostat are also set up accordingly.

Current is sent through the apparatus and the deflection in the galvanometer is noted. Since Kelvin's method is a deflection method, different adjustments are made by making the jockey touch different parts of the wire and the changes in deflection are noted.

Thus, the resistance can easily be determined by noting the readings and then using the equation for finding out the resistance of the galvanometer.