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WHEAT-STONE
BRIDGE
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| 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. |
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BALANCED
WHEAT-STONE BRIDGE
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| 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. | ||||
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VB
– VD = 0
or VB = VD |
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RELATION
AMONG RESISTANCES IN BALANCED CONDITION
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R1/R2
= R3/R4
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EXPRESSION
FOR BALANCED BRIDGE
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| FROM FIGURE: | ||||
R1 & R2 are connected in series. Reason:
(only one path for the flow of current)
R3 & R4 are connected in series.
R1 & R3 are connected in parallel. Reason:
(two paths for the flow of current)
R2 & R4 are connected in parallel.Let current I1 flows through R1 & R2 and I2 through R3 & R4. When bridge is balanced, |
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potential of point ‘B’ = potential of point ‘D’
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| Therefore, | ||||
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VAB = VAD but[V
= IR]
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IR1
= I2R3--------------(I)
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| Similarly, | ||||
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VBC
= VCD
or I1R2 = I2R4------------(II) |
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| Dividing equation (i) by equation (ii) | ||||
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APPLICATIONS
OF WHEATSTONE BRIDGE
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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 |
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Contact
us:
info@citycollegiate.com |
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| For latest information , free computer courses and high impact notes visit : www.citycollegiate.com | ||||