Eddy currents - class-XII

C. LED light.

Inductance Furnace makes use of Eddy current. 

Eddy currents comes in picture only when there is change in linked magnetic flux. 

Eddy currents comes in picture only when there is change in linked magnetic flux. Thus statement A is wrong.

When there is a change in magnetic flux associated with a large piece of metal then currents are induced in that metal these currents are travelling in a closed circular path,  similar to Whirlpools or eddies in water. Such currents are known and Eddy Currents

There is a magnetic loss occur in ferromagnetic material like iron and steel in form of heat these losses are used for induction heating and cooking. For example $\rightarrow$ heating of transformer.

Silicon steel used in lamination mainly reducesHysteresis loss,Eddy current losses,Copper loss. In order to minimize the eddy currents more,magnetic core is laminated . The hysteresis coefficient of silicon steel is less, so hysteresis loss can be reduced. used mainly because of the following advantages: low hysteresis loss. low copper loss due to lower grain resistance.

In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses The losses that can occur in a material are: Iron losses: Iron loss is caused by the alternating flux in the core and consists of hysteresis and eddy current losses. of coercivity on the curve. (The reversed magnetizing force has flipped enough of the domains so that the net flux within the material is zero.)

Eddy currents are produced when the magnetic flux passing through the metal object continuously changes. This may happen due to many reasons:
1) The object is placed in a region with changing magnetic field.
2) The object continuously moves in and out of the magnetic field region (may be uniform or non uniform).

As the magnet falls through the copper tube, changing magnetic flux induces eddy currents in the tube. According to Lenz's law, these eddy currents oppose the motion of the magnet, creating an upward magnetic force. Eventually, this magnetic drag balances gravity, and the magnet falls at a constant terminal velocity.

(A)$P=\dfrac { { \pi  }^{ 2 }{ B } _{ p  }^{ 2 }{ d }^{ 2 }{ f }^{ 2 } }{ 6k\rho D } \ m{ L }^{ 2 }{ T }^{ -3 }=\dfrac { \left( M{ T }^{ -2 }{ A }^{ -1 } \right) ^{ 2 }\left( { L }^{ 2 } \right) \left( { T }^{ -2 } \right)  }{ M{ L }^{ -3 } } \ m{ L }^{ 2 }{ T }^{ -3 }=M{ L }^{ 2 }{ T }^{ -3 }\ m{ L }^{ 2 }{ T }^{ -3 }\neq m{ L }^{ 2 }{ T }^{ -2 }$ where A = amphere, T = Time, L = Length ,M = mass.

The transformer core is laminated to break eddy currents to form loop and hence reducing the power loss due to heat generated due to eddy current.

In general the coil of galvanometer oscillates about it's equilibrium due to rotational inertia which consumes some time. To avoid this coils is bound over  a metallic frame or plate oscillates in a magnetic field the eddy currents generated in the frame or plate oppose the motion and bring the frame to rest as the oscillations die out quickly. This is known as making galvanometer dead beat. 

 It works the same as a disk eddy current brake, by inducing closed loops of eddy current in the conductive rail, which generate counter magnetic fields which oppose the motion of the train.

Eddy currents (also called Foucault currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor due to Faraday's law of induction.