Eddy Current and its Applications
Whenever a large conductor i.e. 2 dimension or 3 dimension conductor in placed in varying magnetic field an EMF is induced in it due to the find closed paths within concentric circular currents known as eddy currents.
Eddy currents by nature are concentric circular currants. Their shape is independent of shape of conductor but as these currants reach may deviate from circular to shape of the conductor.
The plane in which Eddy current are induced is perpendicular to the direction of applied magnetic field.
Eddy current produce heating effect as well as magnetic effects. Eddy currents also obey Leng’s law.
Eddy current is never produced in linear conductor and in 2-d when the conductor in perpendicular to magnetic field and in always produced in 3 –d conductors.
Laminated core :-
Eddy currents are desirable as well as undesirable at times. Is avoid the formation of eddy current a large single conducting piece is replaced by a specially designed piece which is formed by joining this insulated metallic strips such a case is known as Laminated core.
In laminated core the lane of lamina’s is selected in such a way that they are parallel to the applied field as a result formation. It such laminated cases are used in electric motors, generators, transformers, choke ceils etc.
- Induction motor (mechanic effects)
- Induction furnace
- Induction brake → brake on magnetic field produced by eddy currents
- Watt-hour a energy mater (mechanic effects)
- Speedo meter (mechanic effects)
- Dead –beat Galvanometers
Dead beat Galvanometers
On passing current through the galvanometer it’s coil experiences torque and defect to acquire the equilibrium position . on reaching two position although net torque acting on it become zero but it overshoots due to it’s inertia of motion. It stats oscillating about the mean position before coming to rest for quite a long time. In order to avoid such oscillation coil is around over a conducting core which moves in the magnetic field together with the coil due to it’s motion eddy currents are induced in it which according to lenz law oppose the motion therefore oscillation become damped so the coil radically comes to rest at the equilibrium position. Such a galvanometer is known as dead beat galvanometers.
- To obtain liner scale core should be magnetic
- To obtain a dead beat galvanometer core should be conducting
- Soft iron is both magnetic as well as conducting so it’s core makes galvanometer dead beat as well as linear scale galvanometers