Question

What are eddy currents and its applications class 12 notes?

Answer 1

### Eddy Currents: Class 12 Notes

Definition of Eddy Currents:
Eddy currents are loops of electric current induced within conductors when the conductor is exposed to a changing magnetic field. These currents flow in circular paths within the conductor, like eddies in water, hence the name "eddy currents."

Formation of Eddy Currents:

1. When a conductor moves through a magnetic field or when the magnetic field around the conductor changes, the magnetic flux through the conductor changes.
   

1. According to Faraday's Law of Induction, a changing magnetic flux induces an electromotive force (EMF) in the conductor. This induced EMF causes the flow of current within the conductor, forming eddy currents.
   

  

Characteristics of Eddy Currents:

1. Oppose the Change: Eddy currents always oppose the cause of their production, which is in accordance with Lenz's Law.
   

1. Circular Motion: Eddy currents flow in closed loops inside the conductor.
   

1. Heat Generation: Eddy currents cause resistive heating due to the resistance of the material, which can be undesirable in some applications.
   

Mathematical Expression:

The magnitude of induced EMF (\( \epsilon \)) in the conductor can be calculated using Faraday's Law:

\[
\epsilon = - \dfrac{d\Phi_B}{dt}
\]

Where:

1. \( \Phi_B \) is the magnetic flux through the conductor.
   

1. \( \frac{d\Phi_B}{dt} \) is the rate of change of magnetic flux.
   

Factors Affecting Eddy Currents:

1. Magnetic Field Strength: A stronger magnetic field leads to higher induced currents.
   

1. Speed of Movement: Faster motion of the conductor through the magnetic field induces greater currents.
   

1. Conductor's Material: Conductors with higher electrical conductivity tend to have stronger eddy currents.
   

1. Thickness of the Conductor: Thicker conductors lead to stronger eddy currents.
   

Applications of Eddy Currents:

1. Eddy Current Braking:
   

   - Application: Eddy current brakes are used in trains, roller coasters, and in some industrial machines.
   - Working: When a conductor (like a metal disc) moves through a magnetic field, eddy currents are induced. These currents oppose the motion of the conductor, causing it to slow down without physical contact.
   - Advantages: It provides smooth, frictionless braking, with no wear and tear.

1. Induction Heating:
   

   - Application: Used in metal hardening, cooking, and even for forging metals in industries.
   - Working: Eddy currents are induced in a metal workpiece by a changing magnetic field. The resistance to these currents causes the metal to heat up, and this heat is used for various processes like melting or hardening.
   

1. Magnetic Flow Meters:
   

   - Application: Used in fluid flow measurement, especially in pipelines.
   - Working: A magnetic field is applied to a flowing liquid, and eddy currents are induced in the flow. The strength of the eddy currents correlates to the velocity of the flow, which is then measured.

1. Non-Destructive Testing (NDT):
   

   - Application: Eddy current testing is used to detect cracks or flaws in metal structures or components without damaging them (like in aircraft or pipelines).
   - Working: An alternating current is passed through a coil, which generates a changing magnetic field. If there are cracks or faults in the material, they disrupt the eddy currents, causing changes in the signal, which is then analyzed.

1. Induction Motors:
   

   - Application: Induction motors, widely used in household appliances and industrial machines, operate based on the principle of eddy currents.
   - Working: In the rotor of the motor, eddy currents are induced by the rotating magnetic field, which leads to the creation of torque that drives the motor.

1. Electric Meters:
   

   - Application: Eddy currents are used in the working of some electric meters, especially in energy measurement devices.
   - Working: Eddy currents are induced in the metallic discs within the meter. The disc's rotation rate is proportional to the current, allowing for accurate measurement of electrical energy usage.

1. Eddy Current Dampers:
   

   - Application: Used in systems where damping (slowing down or stabilizing movement) is needed, such as in MRI machines or in certain mechanical systems.
   - Working: Eddy currents are generated in a conductive material placed in a magnetic field. These currents oppose the movement, converting kinetic energy into heat and damping the system's motion.

---

Conclusion:

Eddy currents are induced currents that circulate within a conductor when exposed to a changing magnetic field. While they can cause unwanted heat and energy loss, they are utilized in various applications such as induction heating, braking, and non-destructive testing. Understanding the principles of eddy currents is essential for both their beneficial uses and mitigating their adverse effects in electrical systems.