Meter bridge is based on the principle of wheatstone bridge and it is used to find the resistance of an unknown conductor or to compare two unknown
Figure below shows a schematic diagram of a meter bridge
In above figure AC is a 1m long wire made of maganin or constanan having uniform area of cross-section
This wire is stretched along a scale one a wooden base
Ends A and C of the wire are screwed to two L shaped copper strips as shown in figure
A resistance box R and an unknown resistance S are connected as shown in figure
One terminal of galvanometer is connected to point D and another terminal is joined to a jockey that can be slided on a bridge wire
when we adjust the suitable resistance of value R in the resistance box and slide this jockey along the wire then a balance point is obtained sat at point B
Since the circuit now is the same as that of wheatstone bridge ,so from the condition of balanced wheatstone bridge we have
Here resistance P equals
where ρ is the resistivity of the material of the wire and A is the area of cross-section of wire
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