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Induction Motor Interview Questions with Answers | Part-1

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GALVANOMETER

How Galvanometer works??



What is Galvanometer?

  • A galvanometer is a device which is used for detecting and indicating an electric current.
  • It is a one type of electromechanical device.
  • It is used for to indicate the direction of current flow in conductor.
  • A galvanometer is type of Ammeter.

Working Principle

  • Torque acts on a current carrying coil drape in the uniform magnetic field so coil make be rotates.
  • So detection of moving coil galvenogalva is directly proportional to the current flowing in the coil.

Construction

  • The construction of the moving iron galvanometer is shown in below image.


Working

  • Let take a coil PQRS which has L length and width 'b'. It's arrange in a such a way that the plane of coil stay parallel to the magnetic field. Here current through the coil is I.
  • Here coil sides PQ and RS perpendicular to the magnetic field so it's experience the force by each side.
  • F = B I L 
These forces are equal value but direction is opposite so torque tries to deflect the coil. This torque is given by below formula. 
  • T = B I L × b
  • T = B I A              ( L × b = A)
  •  T = n B I A  for n turn coil.

  • Due to this torque the coil plane rotates an angle Ѳ , but magnetic field is radial so this plane is always make be parallel to the magnetic field.
  • So here,
  • T proportional to Ѳ .  So, T = k Ѳ 
  • When equallibrium condition will come so that the restoring torque balance the deflecting torque.
  •   n B I A = k Ѳ 
  • So I proportional to Ѳ 
  • So when current is flow then the moving iron is moved in the direction of current.







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