By learning Physics Topics, we can gain a deeper appreciation for the natural world and our place in it.
What do you Mean by Energy Loss Due to Eddy Currents? How Can the Loss of Energy Due to Eddy Current be Minimised?
To enhance the effect of electromagnetic induction, in many cases solid plates of soft iron or rods are used as the core of the armatures rotating in a magnetic field. For example, in a dynamo (see section 2.1.1 of chapter ‘Alternating current’) the armature rotating in the magnetic field is wound on a core of soft iron. Now, iron is a good conductor of electricity. So electromagnetic induction takes place over the entire volume of the iron rotating in the magnetic field. In fact, many closed circuits or loops are formed locally within iron and induced current continues to
flow in each loop [Fig.(a)], Such current is known as eddy current. Generally eddy current is produced whenever a conducting metal plate is in motion in a magnetic field.
If there is a relative motion between a conducting metal piece and a magnetic field, an induced current is set up throughout the volume of the metal in different closed loops. These current is known as eddy current.
According to Lenz’s law, eddy current opposes the cause that produces it, i.e., it opposes the relative motion between the metallic conductor and the magnetic field. Due to this opposition, heat is generated in the conductor. This wasteful thermal energy comes at the cost of useful energy.
To minimise the loss of energy in the form of heat due to eddy current the cores are not taken as a single piece but are made of many thin laminas of conductors which are insulated from each other with suitable insulating materials [Fig.(b)], By doing so, the flux linked with local eddy current circuits is reduced to a minimum, hence eddy current becomes quite weak and its heating effect is minimised. On calculation it is observed that if the number of lamina be n instead of a single one, the loss of energy due to eddy current will come down to \(\frac{1}{n}\) times.
On the other hand, eddy current in some cases can be applied in favour of us. For example, the coil of a moving coil galvanometer when deflected in the magnetic field begins to oscillate around the equilibrium position. It takes a long time to come to rest. To get rid of this problem the coil is wound on a single soft iron core. The eddy current thus produced in the core opposes the motion of the coil following Lenz’s law. Thus, the coil will not be oscillating for a long time after the current is cut off. It will return to equilibrium position quickly. Besides this, eddy current is employed usefully in induction motor, induction cooker, electric brakes, etc.