QuestionsCh29

# QuestionsCh29 - CHAPTER 29 Electromagnetic Induction and...

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CHAPTER 29: Electromagnetic Induction and Faraday’s Law Responses to Questions 1. Using coils with many ( N ) turns increases the values of the quantities to be experimentally measured, because the induced emf and therefore the induced current are proportional to N . 2. Magnetic flux is a quantitative measure of the number of magnetic field lines passing through a given area. It depends not only on the field itself, but also on the area and on the angle between the field and the area. 3. Yes, the current is induced clockwise. No, there is no induced current if the magnet is steady, because there is no changing flux through the ring. Yes, the current is induced counterclockwise. 4. There is no induced current in the loop that is moving parallel to the wire because there is no change of magnetic flux through the loop. The induced current in the loop moving away from the wire is clockwise. The magnetic field through the loop due to the current is directed into the page, and the loop is moving such that its distance from the wire is increasing, resulting in a decrease in magnetic field strength and therefore a decrease in magnetic flux through the loop. By Lenz’s law, a decreasing magnetic flux into the page results in a clockwise induced current. 5. Yes. The force is attractive. The induced clockwise current in the right loop will induce a counterclockwise current in the left loop which will slow the relative motion of the loops. 6. ( a ) Yes. ( b ) The current starts as soon as the battery is connected and current begins to flow in the first loop. ( c ) The induced current stops as soon as the current in the first loop has reached its steady value. ( d ) The induced current in the second loop will be counterclockwise, in order to oppose the change. ( e ) While there is an induced current, there will be a force between the two loops. ( f ) The force will be repulsive, since the currents are in opposite directions. 7. Yes, a current will be induced in the second coil. It will start when the battery is disconnected from the first coil and stop when the current falls to zero in the first coil. The current in the second loop will be clockwise. 8. Counterclockwise. If the area of the loop decreases, the flux through the loop (directed out of the page) decreases. By Lenz’s law, the resulting induced current will be counterclockwise to oppose the change. Another way to approach this question is to use the right-hand rule. As the bar moves to the left, the negative electrons in the bar will experience a force down, which results in a counterclockwise current.

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• Fall '09
• Thomas
• Current, Magnetic Field, Lenz, eddy currents, N. Magnetic flux

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