Eddy Currents

Induced currents are produced not only in the wires, but also in the block of metals. If a metallic block is placed in a continuously changing magnetic field, induced currents are set up in the body of the metallic block. In the case of the wires the induced current flows along the direction of the wire. How does it flow in metallic blocks? They flow in a circular path by Lenz's law. These current appear like eddies in a fluid and hence are called as eddy current's.

Unlike the metallic wires where the resistance is less metallic blocks have larger resistance and hence the induced currents lead to large amount of Joule's heat (H = i²k).

Sub Topics

Illustration

Illustration

If a bar pendulum is suspended between the pole pieces of a magnet: Let us take another identical pendulum and kept in a field free region. If we oscillate both of them with the same force, it is observed that the one within the field damps faster.

The 'bob' of the pendulum consists of a copper plate. The pendulum is made to swing between the pole pieces of the magnet. Its motion is damped due to eddy currents.

Why does it happen? When the pendulum oscillates inside the field it cuts the magnetic lines of force and hence induces a current in the bar, that is, eddy currents. According to Lenz's laws, the eddy currents oppose the motion and hence produce damping.

Is eddy current advantageous or disadvantageous?

Eddy currents produce a large amount of heat, which is undesirable in a number of cases like dynamos, transformers, where the coil is wound on iron core.

How can eddy currents be minimized?

The solid iron core is divided into a number of thin sheets. The sheets are electrically isolated from each other. These sheets are so placed that the path of the induced eddy currents is broken by the insulating material between the sheets. These are called laminated cores. Hence, using laminated cores can minimize the effects of eddy currents