Meter bridge or slide wire bridge

Meter bridge or slide wire bridge

In this topic we will discuss about Meter bridge or slide wire bridge . Principle of Meter bridge or slide wire bridge  ,  its working and, end errors with correction of end error.

Before to know this topic students must read the following topics.

i. Kirchhoff’s rule , To get the notes of this topic click here-

ii. Wheatstone bridge , To get the notes of this topic click here-

Meter bridge or slide wire bridge –

It is a device used to find the value of unknown resistance . It works on the principle of wheat-stone bridge .

It consist a wire of Constantan or Manganin of one meter length and having uniform area of cross-section . As shown in figure wire is stretched between AC , a cell with a key ‘K’ a resistance box R( known resistance ) is attached and an unknown resistance S  , in two gap as shown in figure .

When switch ‘k’ is on , we start sliding the jockey from A to c , we notice there is a point where galvanometer shows no deflection ( known as null point) . Let this point is at B , let  AB = l

so ,      BC = 100-l

here RAB=ƍl/A ( Where A is the area of cross-section)

RBC = ƍ(100-l)/A

According to wheat-stone bridge principle (P/Q=R/S) We can write

If meter bridge is balanced then R/RAB = S/RBC

Or , R/ ( ƍl/A) = S / ƍ(100-l)/A

Or, R/l =S/(100-l)    so    S = R(100-l)/l ……………eq.

 

To see the video of meter bridge click on the link given below-

 

Error end in the meter bridge- cause of the zero end error is following-

(a) The resistance of the copper strip and connecting wire is not taken in account .

(b)The zero mark of the scale may not start from the position where copper strip leaves the wire and 100 cm  mark may not on the position where the bridge wire just touches the copper strip .

Processes to remove the end error –

By changing the ‘R’ with ‘S’ and ‘S’ with ‘R’ and repeating the experiment . The average value of S determined earlier and now is free from end error .

*** NOTES-  1. Null point ( where galvanometer shows no deflection) should be at the middle of the bridge wire . Because it becomes more sensitive when all four resistances are nearly same.

2.The meter bridge can’t used to measure very high or very low resistance .

  1. the balanced point not effected after interchanging the position of galvanometer and battery .

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