P219lecture11inductors

# P219lecture11inductors - Goal To understand uses for...

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Goal: To understand uses for induction Objectives: 1) To learn how to use Lenz’s Law to determine the direction of an induced current or magnetic field 2) To learn how to use Transformers 3) To learn about Inductors 4) To be able to calculate the Energy stored inside an inductor 5) To learn about LR circuits

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Lenz’s Law V = - N Δ Φ / Δt This is for a coil. If the magnetic field decreases then we will produce a positive EMF. An increase in the magnetic field likewise will produce a negative EMF. The magnetic field induced from the EMF produces a magnetic flux which counteracts the change in magnetic flux! So, when the magnetic field increases (in the + direction) you induce a negative magnetic flux from the current which gives a clockwise current. A decreasing magnetic field (in the + direction) induces a counter-clockwise current (which produces a positive magnetic flux). Note: if you change a negative magnetic field then you have to notice that an increased magnitude is really decreasing the magnetic field. Bottom line is find the current which produces a magnetic field which offsets the change in the magnetic field.
Example: From HW 6: A coil rests upright on your desk. A magnetic field which is at a 90 degree angle to your desk causes a clockwise current in the coil.

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