Question

Kelvin's method of determination of resistance of galvanometer by meter-bridge is​

Answer 1

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• Hint:Kelvin's method determines the resistance of the galvanometer using the principle of Wheatstone bridge, which makes it easier to find the resistance since you only need to know the ratio of the lengths and not the specific value of resistance of wires....

Answer 2

Explanation:

Kelvin's method to determine the resistance of the galvanometer by using a meter bridge:

• A galvanometer whose resistance $'G'$ is to be determined is connected in one gap (left gap) of a Wheatstones meter bridge and a resistance box is connected in the other gap (right gap).

Here, The components represents like follows:

$G:$ Galvanometer

$R:$ Resistance from the resistance box

$AC:$ Metal wire one meter long

$Rh:$ Rheostat

$E:$ Cell

$K:$Plug key

$K:$Jockey

• A cell of emf $'E'$, key $K$ and rheostat $Rh$ is connected in series with the bridge wire $AC.$

• The junction$B$ of the galvanometer and the resistance box is connected to the jockey which can slide along wire $AC.$
• A suitable resistance $K$ is taken in the resistance box and a current $J$ is sent round the circuit.
• Without touching the jockey to any point of $AC,$ note the deflection in the galvanometer.

• A rheostat is adjusted to get a suitable deflection (e.g. $0.15, 20$ divisions) in the galvanometer.

• Place the jockey at points $A$ and $C,$ and see the deflection on the galvanometer. It should be on opposite sides.

• By touching the jockey to different points of wire $AC,$ find (obtain) the point of contact $'D'$ for which the galvanometer shows, the same deflection as before I.e., points $B$ and $D$ are equipotential (i.e. the point gives the same deflection in the galvanometer with or without the contact of the jockey).

• In this method, the null point is not obtained.
• Thus, Kelvin's method is a deflection method.
• The point $D$ is called the balanced point.