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Faraday’s Law

Faraday’s Law. The sliding bar creates an emf by changing the area in the magnetic field. Constant magnetic field The potential was due to the time rate of change of area. Area Change. An emf can also be generated by changing the magnetic field.

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Faraday’s Law

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  1. Faraday’s Law

  2. The sliding bar creates an emf by changing the area in the magnetic field. Constant magnetic field The potential was due to the time rate of change of area. Area Change

  3. An emf can also be generated by changing the magnetic field. The time rate of change of the field through a fixed loop provides the potential. Field Change

  4. The emf depends on the change in field or the change in area. Area perpendicular to the field This suggests that the product of the field and area perpendicular matters. Field Orientation

  5. Magnetic Flux • The product of the field and area perpendicular to the field is the magnetic flux. • The magnetic flux is measured in webers. • 1 Wb = 1 T m2 • The magnetic field can be thought of as a flux density.

  6. The flux can be used to get the induced emf. Sign indicates polarity This is Faraday’s Law of induction. For multiple turns the emf is multiplied. N turns of wire NF is the flux linkage Faraday’s Law

  7. A circular flat coil has 200 turns of wire with a total resistance of 25 W and an enclosed area of 100 cm2. There is a perpendicular magnetic field of 0.50 T that is turned off in 200 ms. Find the current induced in the coil. This problem has three parts. To get the current from the resistance the voltage is needed. To get the voltage the flux is needed. Flux linkage works, too Find the flux first. Coil Flux

  8. The magnetic flux is F= BA. F = (0.50 T)(100 cm2) F = (0.50 T)(0.010 m2) F = 0.0050 T m2 The change in flux is negative since it is turned off. The induced emf is E = -NDF/Dt E = -(200)(-0.0050 Tm2) / (0.20 s) E = DV = 5.0 V The induced current comes from Ohm’s Law. I = V/R I = (5.0 V) / (25 W) I = 0.20 A Flux to Current next

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