Sunday, September 16, 2012

Tangent's Law & Tangent Galvanometer

Tangent's Law

When a small magnet is suspended in two uniform magnetic fields which are at right angles to each other, the magnet comes to rest at an angle θ with respect to B H . This is called the tangent's law.Tangent Galvanometer is a device based on this law.
Prove of Tangent's Law:
  • Anticlockwise Torque = mBH sin(θ)
  • Clockwise Torque = mBsin(90-θ)
  • In equilibrium position:
  • Anticlockwise Torque = Clockwise Torque
  • mBH sin (θ) = mB sin(90-θ)
  • BH tan (θ) = B
  • or tan(θ)= B/BH

Tangent Galvanometer:

It is an instrument which can detect/measure very small electric currents. It is also called as moving magnet galvanometer. It consists of three circular coils of insulated copper wire wound on a vertical circular frame made of nonmagnetic material as ebonite or wood. A small magnetic compass needle is pivoted at the centre of the vertical circular frame. This needle rotates freely in a horizontal plane inside a box made of nonmagnetic material. When the coil of the tangent galvanometer is kept in magnetic meridian and current passes through any of the coil then the needle at the centre gets deflected and comes to an equilibrium position under the action of two perpendicular field : one due to horizontal component of earth and the other due to field set up by the coil due to current (B).

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