12.1 - Lenz's law
- 1. 12.1 – Lenz’s Law and Applications
- 2. Remember this: (from 12.1 – Electromagnetic Induction) As a conductor moves through a magnetic field...... The current that flows makes Fleming’s Left-Hand it’s own force on the Rule force created by the Current conductor. You can use Fleming’s Left Hand Rule to predict it too. This force is in the opposite direction to the motion that Force creating is creating the current! the Motion If there wasn’t an opposing Force being made then once you started pushing the Conductor through the field it would carry on making current for ever with no more force needed. This would contradict the Law of Conservation of Energy
- 3. Lenz’s Law This just says that ‘the direction of the Induced Current is such that it opposes the change that causes it’. ‘If you push a wire through a field the induced current makes a force that pushes back’ ‘If a field is pointing one way and a conductor moves through it, then the induced current makes a field that points the opposite way’
- 4. Faraday’s and Lenz’s Laws – Example 1 A) Faraday’s Law As the magnet approaches the coil the B field increases and the changing flux enclosed by the coil Induces an emf in the coil that causes current to flow. The size of the emf is equal to the rate of change of the flux enclosed by the coil.
- 5. Faraday’s and Lenz’s Laws – Example 1 B) Lenz’s Law The direction of the Induced current is such that it opposes the change producing it (the magnet moving towards the coil) The current in the coil has to make a magnetic field that pushes the Magnet away.... The Right hand grip rule shows how the current must flow.
- 6. Faraday’s and Lenz’s Laws – Example 2 A) Faraday’s Law When the current in circuit A flows, a magnetic field is created which causes the magnetic flux enclosed by the coil in Circuit B to increase. This increasing flux induces a current in coil B. It only happens for a milli- second when it is switched on. After that the flux is constant so there is no induced current.
- 7. Faraday’s and Lenz’s Laws – Example 2 B) Lenz’s Law The direction of the current in B must oppose the change producing it (the increasing field from A). To do this the current induced in B flows to create a Magnetic field in the opposite direction to that from A this is how a transformer works
- 8. Magnet in Copper Pipe Faraday’s Law As the magnet falls through the copper pipe there is a changing Flux on the copper. This induces eddy currents in the copper pipe. http://www.youtube.com/watch?feature=player_ embedded&v=dnK6oxbPSM4 Lenz’s Law The eddy currents flow in such a way that they create a magnetic field which opposes the change that produced them. http://www.youtube.com/watch?v=otu-KV3iH_I
- 9. Induction Braking – Eddy current braking Faraday’s Law As the magnet is brought near to the rotating disc there is a changing Flux on any point in the copper. This induces eddy currents in the copper disc. Lenz’s Law The eddy currents flow in sucha http://www.youtube.com/watch?v=SK0EdikjC24&featur way that they create a magnetic e=related field which opposes the change that produced them. The Railway Gazette http://www.railwaygazette.com/news/sing le-view/view/eddy-current-braking-a-long- road-to-success.html http://demonstrations.wolfram.com/MagneticBraking/ You might need the Wolfram plugin for this to work
- 10. Induction Braking – Eddy current braking Foucault’s Disc – a simulation http://www.magnet.fsu.edu/education/tutorials/java/foucaultdisk/index.html
- 11. Quantum Levitation & Flux Pinning Superconducting Disc The upper disc is a superconductor in which an Induced Current is created by the changing flux as it is brought near to the lower magnet. This induced current flows constantly because the superconductor has zero resistance http://www.youtube.com/watch?v=Ws6AAhTw7RA Lenz’s Law The induced currents flow in Explanation such a way that they create a magnetic field which opposes the change that produced them. http://www.divshare.com/download/17914105-09c Flux Pinning http://en.wikipedia.org/wiki/Flux_pinning