Question 11: Explain eddy current with suitable example. How eddy currents can be minimized?
Eddy currents are currents induced in metals moving in a magnetic field or metals that are exposed to a changing magnetic field.
Explanation of eddy currents
Consider a solid metallic cylinder rotating in a magnetic field as shown in the figure below.
Let ∆Ф is the change in the magnetic flux during time ∆t. The induced emf is then,
Similarly, if R is the resistance of the metallic cylinder, then the eddy current produced is given by
The direction of the eddy current is determined by the Lenz law. It would be such that the magnetic field produced due to eddy current would oppose the cause which produces it which is the change in the magnetic flux. Therefore, the magnetic force due to the eddy currents will be such to resist the rotation of the cylinder.
Technique of minimizing eddy currents
Eddy currents have a major drawback of producing heat. The heat produced (I2Rt) is usually big enough to cause damage. Therefore, it is important to reduce eddy currents in such cases.
One method to reduce the unwanted effects of eddy currents is using a laminated conductor. A laminated substance is one which is built in thin sheets or layers that have been bonded together with some insulating adhesive (glue) or under heat. The insulation between the sheets increases the resistance of the conductor and thus reducing the amount of current. The reduced amount of current then produces less heat loss.