Meter Bridge | Principle | Formula

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Wheatstone Bridge-

 

Before you go through this article, make sure that you have gone through the previous article on Wheatstone Bridge.

 

We have learnt-

  • A Wheatstone bridge is an arrangement of four resistances used to determine one of these resistances in terms of the remaining three resistances.
  • It is a null method and is preferred over the other methods for determining the value of an unknown resistance.

 

In this article, we will learn about Meter Bridge.

 

Meter Bridge-

 

Meter bridge is the practical application of the Wheatstone bridge that is used to measure an unknown resistance.

 

Principle-

 

Its working is based on the principle of Wheatstone bridge. When the bridge is balanced, we have-

 

 

Construction-

 

  • It consists of a one meter long manganin wire of uniform cross-section.
  • The wire is stretched along a meter scale fixed over a wooden board.
  • The two ends of the wire are soldered to two L-shaped thick copper strips A and C.
  • Between these two copper strips, another copper strip is fixed so as to provide two gaps.
  • A resistance box is connected in one gap and the unknown resistance in the other gap.
  • A source of emf E is connected across AC.
  • A movable jockey and a galvanometer are connected across BD as shown in the figure.

 

METER BRIDGE

 

Working-

 

  • A suitable resistance R is taken out from the resistance box.
  • Then, the jockey is moved along the wire AC till there is no deflection in the galvanometer.
  • This is the balanced condition of the Wheatstone bridge.

 

If P and Q are the resistances of the parts AB and BC of the wire, then for the balanced condition of the Wheatstone bridge, we have-

 

 

Let AB = ℓ cm, then BC = (100 – ℓ) cm.

Since the wire is of uniform cross-section, therefore-

Resistance of wire ∝ Length of wire

 

 

where σ is the resistance per unit length of the wire.

 

Hence,

 

From here,

 

Knowing the values of ℓ and R, the value of unknown resistance S can be determined.

 

Determination of Resistivity-

 

If r is the radius of the wire and L is its length, then resistivity of its material is given by-

 

 

Test Your Concepts-

Quiz on Meter Bridge

 

Next Article-

Electric Cells & Batteries

 

Get more notes & other study material of the Chapter Current Electricity.


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