## Presentation on theme: "Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electromagnetic induction Lenz’s law Faraday’s law The nature of electromagnetic."— Presentation transcript:

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electromagnetic induction Lenz’s law Faraday’s law The nature of electromagnetic waves The spectrum of electromagnetic waves Electromagnetic Induction and Electromagnetic Waves Topics: Sample question: The ultraviolet view of the flowers on the right shows markings that cannot be seen in the visible region of the spectrum. Whose eyes are these markings intended for? Slide 25-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding A loop of wire of area A is tipped at an angle to a uniform magnetic field B. The maximum flux occurs for an angle. What angle will give a flux that is ½ of this maximum value? A. B. C. D. Slide 25-11

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A loop of wire of area A is tipped at an angle to a uniform magnetic field B. The maximum flux occurs for an angle. What angle will give a flux that is ½ of this maximum value? C. Slide 25-12 Answer

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 21.5 Electric Generators A generator is the opposite of a motor – it transforms mechanical energy into electrical energy. This is an ac generator: The axle is rotated by an external force such as falling water or steam. The brushes are in constant electrical contact with the slip rings.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 21.5 Electric Generators A dc generator is similar, except that it has a split-ring commutator instead of slip rings.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 21.5 Electric Generators A sinusoidal emf is induced in the rotating loop ( N is the number of turns, and A the area of the loop): (21-5)

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A long conductor carrying a current runs next to a loop of wire. The current in the wire varies as in the graph. Which segment of the graph corresponds to the largest induced current in the loop? Slide 25-16 Checking Understanding

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A long conductor carrying a current runs next to a loop of wire. The current in the wire varies as in the graph. Which segment of the graph corresponds to the largest induced current in the loop? Slide 25-17 Answer

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Lenz’s Law Slide 25-13 Lenz’s law There is an induced current in a closed, conducting loop if and only if the magnetic flux through the loop is changing. The direction of the induced current is such that the induced magnetic field opposes the change in the flux.