Wheat stone bridge

Wheat stone bridge

  • Wheat stone bridge was designed by British physicist sir Charles F Wheatstone in 1833
  • It is a arrangement of four resistors used to determine resistance of one resistors in terms of other three resistors
  • Consider the figure given below which is an arrangement of resistors and is knowns as wheat stone bridge

    Wheat stone bridge

  • Wheatstone bridge consists of four resistance P,Q,R and S with a battery of EMF E.Two keys K1 and K2 are connected across terminals A and C and B and D respectively
  • ON pressing key K1 first and then pressing K2 next if galvanometer does not show any deflection then Wheatstone bridge is said to be balanced
  • Galvanometer is not showing any deflection this means that no current is flowing through the galvanometer and terminal B and D are at the same
    potential .THus for a balanced bridge
  • Now we have to find the condition for the balanced Wheatstone bridge .For this applying Kirchhoff's loop rule to the loop ABDA ,we find the relation
    or I1P=I2R --(a)
    Again applying Kirchhoff's rule to the loop BCDB
    or I1Q=I2S --(b)
    From equation a and b we get
    P/Q=R/S                       (12)
  • equation 12 gives the condition for the balanced Wheatstone bridge
  • Thus if the ratio of the resistance R is known then unknown resistance S can easily be calculated
  • One important thing to note is that when bridge is balanced positions of cell and galvanometer can be exchanged without having any effect on the balance of the bridge
  • Sensitivity of the bridge depends on the relative magnitudes of the resistance in the four arm of the bridge is maximum for same order of four resistance.

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