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
resistance
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
P/Q=R/S
Here resistance P equals
P=ρl1/A
And Q=ρl2/A
where ρ is the resistivity of the material of the wire and A is the area of cross-section of wire
Now P/Q=(ρl1/A)(A/ρl2)=l1/l2
