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Problems 957 27. Explain why it is desirable to use hard ferromagnetic materials to make permanent magnets. 28. Would you expect the tape from a tape recorder to be attracted to a magnet? (Try it, but not with a recording you 29. Given only a strong magnet and a screwdriver, how would you first magnetize and then demagnetize the screwdriver? 30. Which way would a compass point if you were at the north magnetic pole of the Earth? 31. Figure Q30.31 shows two permanent magnets, each having a hole through its center. Note that the upper magnet is Figure Q30.31 Courtesy of Central Scientific Company Section 30.1 The Biot–Savart Law 1. In Niels Bohr’s 1913 model of the hydrogen atom, an ' 11 m with a speed of 2.19 & 10 6 m/s. Compute the magnitude of the magnetic field that this motion produces at the 2. A lightning bolt may carry a current of 1.00 & 10 4 A for a short period of time. What is the resulting magnetic field (a) A conductor in the shape of a square loop of edge 3. 4. Calculate the magnitude of the magnetic field at a point 100 cm from a long, thin conductor carrying a current of Determine the magnetic field at a point P located a distance x from the corner of an infinitely long wire bent 5. 1, 2 , 3 = straightforward, intermediate, challenging = full solution available in the Student Solutions Manual and Study Guide = coached solution with hints available at http://www.pse6.com = computer useful in solving problem = paired numerical and symbolic problems P R O B L E M S I ! Figure P30.3 Figure P30.5 x P I I 6. A conductor consists of a circular loop of radius R and two Figure P30.6 I = 7.00 A |