CHAPTER 21
Discussion Questions
4. An electric door bell is basically an automatically interrupted electromagnet. Referring to Fig. Q4, describe how it works.
Problems
36. A small ball of plastic carries a positive charge and is shot at high speed along the x-axis in the horizontal x-y plane. It passes through an uniform horizontal B-field, which makes an angle with the x-axis of +23.5 degrees. In what direction is the magnetic force it will experience?
39. A proton in a research facility is properlled at 2,000,000 m/s perpendicular to an uniform magnetic field. If it experiences a force of 4 x 10**(-13) N, what is the strength of the field?
48. A 10-m long wire is strung more or less horizontally in an east-west direction, and a current of 10 A is sent from west to east along it. Assuming the Earth's B-field at that location has a magnitude of 0.00005 T and is horizontal and due north, find the magnitude of the force on the wire.
52. A narrow flat coil wound on a square frame has 200 turns and sides of 20 cm. It carries a current of 1.25 A and is positioned in a 0.50 T magnetic field.What is the maximum torque that can be exerted by the field on the coil?
54. Two parallel wires 50.0 m long are 25.0 cm apart and each carries a current of 10 A in the same direction. What is the force (magnitude and direction) between them?
56. A cosmic ray proton traverses an uniform B-field perpendicularly at a speed of 20,000,000 m/sin the positive x-direction, experiencing an accleration of 4.0 x 10**(12) m/s**2 in the positive y-direction. Determine B.
65. In a moving coil galvanometer, the coil, which has N turns, surrounds a steel core so that the B-field always makes an angle of 60 degrees with the symmetry acis (the z-axis). If the current through the coil is reduced by 25 %, how does the torque on it change?
66. A single circular hoop of write 10 cm in radius is hung on a fine silver ribbon so that the plane of the loop is parallel to the magnetic field in a uniform region between the pole pieces of a large electromagnet. If the torque on the coil is 0.100 N-m when 5.0 A pases through the coil, what is the magnitude of the B-field?