Chapter 29 Electromagnetic Induction & Faraday’s Law

Introduction Our approach –What is electromagnetic induction? Faraday’s Law Lenz’s Law –Applications and consequences EMF induced in a moving conductor Electric generators Back EMFs & counter torques Eddy currents Transformers & power transmission –E-field with a changing B-field

Electromagnetic Induction What do we mean by electromagnetic induction? Sketch an example Make induction happen with equipment given; draw some conclusions

Faraday’s Law of induction What is magnetic flux (in words and mathematically)? What is the relation between magnetic flux and induced emf? (mathematically and in words) What are some examples of ways a changing magnetic flux induces an emf?

Lenz’s Law What is the direction of the induced current? That is, how does the direction depend on the physical situation that induces the current? What are some examples of the behavior described by Lenz’s Law? Precisely state Lenz’s Law.

EMF induced in moving conductor How is an emf induced in a conductor moving in a magnetic field? (Sketch a picture and describe this phenomenon.) What is the mathematical relationship among relevant quantities in this situation? How is a current induced in a conductor moving in a magnetic field? (Sketch a picture and describe this phenomenon.)

EMF induced (cont’d) How much force is needed to move the conductor (when one side of a rectangular loop moves) to cause the current? How is this consistent with conservation of energy?

Electric Generators In general, how do generators work? In general, what’s the main difference between dc and ac generators? In general, what’s the main difference between a dc generator and an alternator?

Back EMF & Counter Torque What is back emf, and how in general does it arise in a motor? What is motor overload, and how is it understood in terms of back emf? What is counter torque, and how in general does it arise in a generator?

Eddy Currents What are eddy currents, and how do they arise? How are eddy currents used? – metals/eddy_current.phphttp:// metals/eddy_current.php How are they minimized?

Transformers & Power Transmission What is a transformer? (Make a sketch) How is the transformer equation derived? What assumptions go into deriving the transformer equation? What is meant by “step-up” and “step- down” transformers, and how in general is this difference produced? How and why are transformers used?

Electric Field from Changing Magnetic Field Using the fact that an emf is related to an electric field, re-express Faraday’s Law in terms of the electric field. How is this relation more general? What is the electric field produced between the circular poles of an electro- magnet with alternating current? Are electrical forces due to changing magnetic fields conservative? Explain.

The end