======Eddy Currents and Magnetic Damping======


<WRAP right box>
**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
\\
**Categories:** {{$demo.categories}}
\\


**Alternative titles:** Magnetic Braking with Eddy Currents
</WRAP>

====Summary====                   
{{$demo.summary}}



====Procedure====  
  - Suspend a flat metal plate as a pendulum and position it so that it swings between the poles of a strong magnet. Observe that its motion is quickly damped.
  - Replace the solid plate with a slotted metal plate. Swing it again and note that damping is much weaker because eddy currents are restricted.
  - Replace the plate with a nonconducting material (e.g., plastic or wood) and observe negligible damping, since almost no eddy currents are induced.
  - Ask students to predict current directions using Faraday’s law and Lenz’s law: as the plate enters the field, induced currents oppose the change in flux; as it leaves, currents reverse but still oppose motion.
  - Discuss how slots or laminated construction reduce eddy currents and are used in real devices.



====Links==== 
Faraday's Law Demo: Eddy Pendulum - Physics Demos: 
{{youtube>0b0V0impJ_E?}}\\

Eddy Currents and Magnetic Braking of a Pendulum Caused by Electromagnetic Induction - Electric and Magnetic Fields: 
{{youtube>MglUIiBy2lQ?}}\\

====Variations====
  * Test plates of different metals (copper, aluminum, steel) to compare conductivity and damping strength.
  * Try thicker versus thinner plates to show how plate geometry affects damping.
  * Use a rotating conducting disk in a magnetic field to model how induction brakes work.
  * Demonstrate induction heating by placing a ferromagnetic cooking pot on an induction cooktop and explaining the role of eddy currents.



====Safety Precautions====
  * Keep fingers clear of the pendulum swing and strong magnets.
  * Handle strong rare-earth magnets with care to avoid pinching or sudden attraction.
  * Do not place magnets near electronic devices, bank cards, or medical implants.
  * Ensure pendulum setup is stable so the magnet does not tip or fall.




====Questions to Consider====
  * Why do eddy currents oppose the motion of the plate? (Lenz’s law: the induced current creates a magnetic field opposing the change in flux.)
  * Why does a slotted plate reduce magnetic damping? (Slots break up current loops, reducing their size and effectiveness.)
  * Why is there no damping when the plate is fully inside the uniform magnetic field? (No flux change occurs, so no current is induced.)
  * Why does an insulating plate experience negligible damping? (No mobile charges exist to form currents.)
  * How does magnetic damping help improve sensitive balances? (It reduces oscillations quickly without adding friction.)
  * Why can eddy currents slow but not fully stop a moving object, like a train? (The damping force decreases with speed and approaches zero as motion slows.)