12.1 - Faraday's law


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  • Hi, there is something about Faraday's Law that is confusing me: Is it the length of coil that determines voltage output or the area of the coil in contact with magnetic flux?
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12.1 - Faraday's law

  1. 1. 12.1 - Electromagnetic Induction
  2. 2. Describing the Inducing of EMF – learn these steps 1. Conductor moving in a magnetic field If a conductor moves at a speed v through a magnetic field, the electrons inside it receive a force due to their Motion in the Magnetic field. Remember that electrons moving downwards are like current flowing upwards. Use Fleming’s Left Hand Rule to predict which way they will move The electrons move towards the left side of the conductor shown in this picture.
  3. 3. Describing the Inducing of EMF – learn these steps 2. An Induced EMF is created Because the Charges are separated it creates a Potential Difference between the two ends. The Charges would ‘like’ to move back but can’t because of the Magnetic Field and the Motion of the conductor which are combining to move them apart. If an external circuit is connected they will flow through it to get to the lower potential.
  4. 4. Describing the Inducing of EMF – learn these steps 3. Conservation of Energy Fleming’s Left-Hand The current that flows makes Rule force created by it’s own force on the 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
  5. 5. Describing the Inducing of EMF – learn these steps 4. Calculating the Induced EMF Force on charge in B-Field This is known as the Induced EMFElectric Field Strength Definition
  6. 6. Flux Density (B) & Flux (Φ) Magnetic Flux Density (B) This is just a measure of the closeness of the field lines, or the field lines per unit area Flux (Φ) This is the sum of all the flux density (field lines per unit area) in an Area. Φ=BA Most people find the idea of Flux Φ really hard to understand
  7. 7. Flux (Φ).... continued Going back to:
  8. 8. Faraday’s LawFaraday’s Law just puts all of these ideas in one simpleequation: emf = Rate of Change of flux Sometimes an E or Ԑis used for EMF
  9. 9. Faraday’s Law Simulations Faraday’s Law on PhET http://phet.colorado.edu/en/simulation http://phet.colorado.edu/en/simulation/farada /faraday ys-lawUse these to help you understand the ideas behind Faraday’s Law
  10. 10. Extra Facts 1: Fleming’s Right Hand RuleFleming’s Right Hand Rule gives the direction of the Induced (made) Currentif we know the Motion and the Field.
  11. 11. Extra Facts 2 - Non-Perpendicular B-Fields
  12. 12. Extra Facts 3 - CoilsFaraday’s Law:Changes for ‘N’ coils andbecomes:
  13. 13. What does it all mean?Faraday’s Law?