wheat stone bridge

Asked by ANAGHA AV | 14th May, 2012, 07:56: PM

Expert Answer:

 
Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of abridge circuit, one leg of which includes the unknown component.
 
 
Wheat stone bridge is an electrical circuit . In wheat-stone bridge four resistance R1, R2, R3 and R4 are connected end to end with each other to form a closed loop. A sensitive galvanometer "G" is connected between their junctions as shown . The circuit is provided with two keys ‘K1’ and ‘K2’.
Generally wheat-stone bridge is used to determine unknown resistances.

 
BALANCED WHEAT-STONE BRIDGE
 
  When ‘K1’ is connected, no current passes through the galvanometer because K2 is disconnected. When ‘K1’ and ‘K2’ are connected and no current flows through the galvanometer, the condition of bridge is called "Balanced condition". It is possible only when the potential difference between the terminals of galvanometer is zero or potential of point ‘B’ = potential of point ‘D’ i.e.
V– V= 0 
or 
V= VD
 

 
RELATION AMONG RESISTANCES IN BALANCED CONDITION
 
R1/R= R3/R4
EXPRESSION FOR BALANCED BRIDGE
 
FROM FIGURE:
 R1 & R2 are connected in series.           Reason: (only one path for the flow of current)
 R& Rare connected in series.
 R& R3 are connected in parallel.         Reason: (two paths for the flow of current)
 R& R4 are connected in parallel.
Let current I1 flows through R& R2 and Ithrough R& R4.
When bridge is balanced,
potential of point ‘B’ = potential of point ‘D’
Therefore,
                           VAB = VAD                    but[V = IR]
               IR= I2R3--------------(I)
Similarly,
VBC = VCD       
or 
               I1R= I2R4------------(II)
Dividing equation (i) by equation (ii)
APPLICATIONS OF WHEATSTONE BRIDGE
 
A number of resistance measuring devices have been devised on the principle of wheatstone bridge.For example :
 Meter bridge
 Post office box
 Potentiometer
 Carey Foster's bridge
 Callendar bridge
 Griffith's bridge

Answered by  | 15th May, 2012, 09:24: AM

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