# E&M REVIEW FARADAY AND LENZ’S LAW DEAN CLARKE, NICK ROJVALL, JUSTINE THOMPSON.

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E&M REVIEW FARADAY AND LENZ’S LAW DEAN CLARKE, NICK ROJVALL, JUSTINE THOMPSON

BIG IDEAS Faraday- If the magnetic flux through an area bounded by a closed conducting loop changes with time, a current and an emf are produced in the loop. This is called induction Induced emf is related to change in magnetic flux. Field intensity is inversely related to distance

BIG IDEAS CONT’D. If a magnet is stationary relative to a loop, no current is induced Induced current will be in a direction that will oppose the change in magnetic flux Ex: If magnetic flux is decreasing, a current will be induced do that its B-field will add to the original B-field and oppose the change in flux and vice versa.

RELEVANT FORMULAE

RELEVANT FORMULAE CON’T

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Conductor moving in magnetic field v F=qvB ---- +++ F=qE L As a conductor moves through a B-field, charges separate due to magnetic force. The separation of charge creates a uniform e-field within the conductor. Wire is in electromagnetic equilibrium when The presence of an e-field creates a potential difference between the ends of the conductor. (Since –ive charges accumulate at the lower end, the upper end is at a higher electric potential. A voltage is “induced” by the motion.)

PRACTICE PROBLEM An elastic conducting material is stretched into a circular loop of radius 12 cm and placed parallel to a magnetic field of strength B =.8 T. The material is then released and its radius begins shrinking at an instantaneous rate of 75 cm/s. What emf is induced in the material the instant it is released?

PRACTICE PROBLEM A metal rod moves with a constant velocity along two parallel metal rails as shown in the diagram. A magnetic field B =.350 T is directed out of the page. If L = 25 cm, and v = 55 cm/s, what emf is generated in the loop? If the rod has a resistance of 18Ω and resistance in the rail and end connector are negligible what current will be generated through the rod? vVvV B (out of the page) L