ism_ch23

# ism_ch23 - Chapter 23 Magnetic Flux and Faraday's Law of...

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96 Chapter 23 Magnetic Flux and Faraday’s Law of Induction Answers to Even-numbered Conceptual Questions 2. The magnetic field indicates the strength and direction of the magnetic force that a charged particle moving with a certain velocity would experience at a given point in space. The magnetic flux, on the other hand, can be thought of as a measure of the “amount” of magnetic field that passes through a given area. 4. The magnetic flux through the loop of wire is greatest when its normal points vertically downward, because in this case the normal points in almost the same direction as the magnetic field. There is little magnetic flux through the loop if its normal is horizontal; that is, when its normal is essentially at right angles to the field. 6. When the disk is at its maximum displacement to the right, it is well within the region of uniform magnetic field. Therefore, the magnetic flux through the disk is not changing. It follows, then, that the induced current at this point is a minimum; namely, zero. 8. The magnetic field will have little apparent effect, because the break in the ring will prevent a current from flowing around its circumference. What the magnetic field will do, however, is produce a nonzero emf between the two sides of the break. 10. Nothing. In this case, the break prevents a current from circulating around the ring. This, in turn, prevents the ring from experiencing a magnetic force that would propel it into the air. 12. No. The fact that the two wires are not connected means that no current can flow through the rod. As a result, the magnetic field exerts zero force on the rod. If the system is frictionless, no force will be required to keep the rod moving with a constant speed. 14. As the penny begins to tip over, there is a large change in the magnetic flux through its surface, due to the great intensity of the MRI magnetic field. This change in magnetic flux generates an induced current in the penny that opposes its motion. As a result, the penny falls over slowly, as if it were immersed in molasses. 16. Initially, the rod accelerates to the left, due to the downward current it carries. As it speeds up, however, the motional emf it generates will begin to counteract the emf of the battery. Eventually the two emfs balance one another, and current stops flowing in the rod. From this point on, the rod continues to move with constant speed. 18. When the angular speed of the coil in an electric generator is increased, the rate at which the magnetic flux changes increases as well. As a result, the magnitude of the induced emf produced by the generator increases. Of course, the frequency of the induced emf increases as well. 20. The energy stored in the inductor remains the same. Doubling the number of turns per length quadruples the inductance of the solenoid, as we can see from Equation 23-14. The energy stored in an inductor, however, depends on both the inductance of the inductor and the current it carries, as we see in Equation 23-19. In fact, the energy stored in an inductor depends on the square of the current.

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## This note was uploaded on 04/08/2008 for the course PHYS 104 taught by Professor Pengyi during the Fall '08 term at UNC.

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ism_ch23 - Chapter 23 Magnetic Flux and Faraday's Law of...

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