chapter 29 pt 2

29.9

9. | Although the evidence is weak, there has been concern in re- BIU cent years over possible health effects from the magnetic fields generated by electric transmission lines. A typical high-voltage transmission line is 20 In above the ground and carries a 200 A current at a potential of 110 kV. a. What is the magnetic field strength on the ground directly under such a transmission line? b. What percentage is this of the earth's magnetic field of 50 \"T? 31. || The microwaves in a microwave oven are produced in a spe- cial tube called a magnetron. The electrons orbit the magnetic field at 2.4 GHz, and as they do so they emit 2.4 GHz electro- magnetic waves. a. What is the magnetic field strength? b. If the maximum diameter of the electron orbit before the elec- tron hits the wall of the tube is 2.5 cm, what is the maximum electron kinetic energy? 55. || The toroid of FIGURE P2955 is a coil of wire wrapped around a doughnut-shaped ring (a torus). Toroidal magnetic fields are used to confine fusion plasmas. a. From symmetry, what must be the shape of the magnetic field in this toroid? Explain. b. Consider a toroid with N closely spaced turns carrying current I. Use Ampere's law to find an expression for the magnetic field strength at a point inside the torus at distance r from the axis. c. Is a toroidal magnetic field a uniform field? Explain. FIGURE P2955 FIGURE P2956 U 63. II An antiproton is identical to a proton except it has the opposite charge, e. To study antiprotons, they must be confined in an ultrahigh vacuum because they will annihilateproducing gamma raysif they come into contact with the protons of ordinary matter. One way of confining antiprotons is to keep them in a magnetic field. Suppose that antiprotons are created with a speed of 1.5 X 10'4 m/s and then trapped in a 2.0 mT magnetic field. What minimum diameter must the vacuum chamber have to allow these antiprotons to circulate without touching the walls