8B - 9 Induction_11 - Electromagnetic Induction Electric...

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Unformatted text preview: Electromagnetic Induction Electric currents produced by changing magnetic fields - changes the world Michael Faraday, 1791 - 1867 Arguably the greatest experimentalist of modern times. His words to give us courage: "The world little knows how many of the thoughts and theories which have passed through the mind of the scientific investigator have been crushed in silence and secrecy by his own severe criticism and adverse examination; that in the most successful instances not a tenth of the suggestions, the hopes, the wishes, the preliminary conclusions have been realized."- Or, as a cartoonist sees it "What's the opposite of 'Eureka'?" Cartoon by George Abbott Faraday s Experiments Changing magnetic field induces a flow of electric charge in a loop. Id say its the most important practical discovery in the past 200 years. Faraday s Law of Induction An emf is induced in the loops at the left when the number of magnetic lines that pass through the loop is changing. The actual number of field lines passing through the loop does not matter; the values of the induced emf and induced current are determined by the rate at which that number changes . CHECKPOINT The graph gives the magnitude B ( t ) of a uniform magnetic field that exists throughout a conducting loop, with the direction of the field perpendicular to the plane of the loop. Rank the five regions of the graph according to the magnitude of the emf induced in the loop, greatest first. b, d=e, a=c = 0 The direction of induced current - Lenzs Law An induced current has a direction such that the magnetic field due to the induced current opposes the change in the magnetic flux that induces the current. Example of Lenz s Law Opposition to Pole Movement. The approach of the magnet's north pole increases the magnetic flux through the loop and thereby induces a current in the loop. We know thatinduces a current in the loop....
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8B - 9 Induction_11 - Electromagnetic Induction Electric...

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