question_answer

Direction: Q.21 to Q.25

An eddy current is a current set up in a conductor in response to a changing magnetic field. They flow in closed loops in plane perpendicular to the magnetic field. By Lenz's law, the current swirls in such a way as to create a magnetic field opposing the change; for this to occur in a conductor, electrons swirl in a plane perpendicular to the magnetic field.

Because of the tendency of eddy currents to oppose, eddy currents cause a loss of energy. Eddy currents transform more useful forms of energy. Eddy currents can also be removed by cracks or slits in the conductor, which break the circuit and prevent the current loops from circulating. This means that eddy currents can be used to detect defects in materials. This is called non destructive testing and is often used in airplanes. The magnetic field produced by the eddy currents is measured, where a change in the field reveals the presence of an irregularity a defect will reduce the size of the eddy current, which in turn reduces the magnetic field strength.

Another application of eddy currents is magnetic levitation. Conductors are exposed to varying magnetic fields which induce eddy currents within the conductor and produce a repulsive magnetic field, pushing the magnet and conductor apart. This alternating magnetic field can be caused by relative motion between the magnet and conductor (generally the magnet is stationary and the conductor moves) or with an electromagnet applied with a varying current to very the magnetic field strength.

Read the above passage carefully and give the answer of the following questions:

What is the heat generated in eddy current operations?

A) \[Vl\]                            

B) \[VlR\]

C) \[{{l}^{2}}RT\]           

D)             \[{{l}^{2}}R\]