Question

meter bridge formula

Answer 1

How is a Meter Bridge used in Calculating the Unknown Resistance?

A meter bridge is an apparatus utilized in finding the unknown resistance of a coil. The below figure 12 is the diagram of a useful meter bridge instrument.

In the figure, R is called as the Resistance
P is the Resistance coming across AB
S is the Unknown Resistance
Q is the Resistance between the joints BD
AC is long wire of length a 1m made of constantan or manganin having a uniform area of the cross-section Such that L1+L2=100
Assuming that L1=L => L2=100-L

Relation obtains the unknown resistance ‘X’ of the given wire:
X = RL2/L1= R(100-L) /L

And the specific resistance of material for a given wire is obtained by the relation=(3.14) r2X/l
where, r = the radius of the cable and also l = length of the wire.

The devices required in finding the unknown resistance of a conductor using a meter bridge are-
Meter bridge
Resistance box
Galvanometer
Unknown Resistance of a length 1 m
Screw gauge
connecting Wires
Jockey
One way key
In the meter bridge, one of the lateral kinds of resistances is replaced by a wire having a length of the uniform cross section of about 1m. The other pair consists of one known and an unknown pair of resistances. The one part of the galvanometer is connected in between the both resistances, whereas the other part of the wire is finding the null point where the galvanometer is not showing any deflection. At this point, the bridge is said to be balanced.

Answer 2

Rx = R(100- lx)/lx......