Discussion Questions:
9. Figure Q9 shows a 70-kV, 60 Hz power line in a remote area of the countryside. A shifty local resident has erected a large open loop just below the line with the intention of drawing off power. Is this possible and, if so, how would it be transferred? Where would the energy stolen come from? Would anyone be able to detect the loss? Might it be possible to bug a telephone using the same approach? Explain.
16. Figure Q16 shows an electron orbiting between the poles of an electromagnet in a device called a betatron. The field is gradually begin increased. How does the machine accelerate the electron? What keeps it in orbit?
Problems:
2. An uniform magentic field of 100 mT passes through a loop of wire having an area of 0.020 m**2. The field makes an angle of 30 degrees with the perpendicular to the plane of the loop. What is the magnetic flux through the loop?
7. A single loop of wire with an encompassed area of 0.25 m**2 is perpendicular to a 0.40-T uniform magnetic field. The loop is uanked from the field in 200 ms; what is the induced emf?
8. A 100-turn coil of wire is removed laterally from an axial B-field in 20 ms, and an emf of 1.0 V is induced across it in the process. How big was the field if the cross-sectional area of the coil is 4.0 cm**2?
12. A 10-turn coil of wire of area 0.25 m**2 is in a perpendicular magnetic field that changes in times as illustrated in Fig P12. Determine the induced voltage across the loop as a function of time.
16. An emf of 0.45 V is induced in a straight conductor having a length of 20 cm moving at right angles to a magnetic field at a constant speed of 600 cm/s. Calculate the value fo the field.
21. Imagine a vertical magnetic field decreasing at a constant rate of 20 mT/s. A flat circular coil of 220 turns with a 20-cm diamter has 30 micro-F capacitor across its terminals. If the coil is placed perpendicular to the field, what is the steady-state charge on the capacitor?
23. A single loop of copper wire in the shape of a square 4.0 cm on each side is lying flat on a horizontal table. A large electromagnet is positioned with its north pole above and to the left a little so that the uniform magnetic field is downward into the loop, amaking an angle of 30 degrees with the vertical. Compute the average induced emf across the loop as the field varies linearly from 0 to its final value of 0.500 T in 200 ms. What is the direction of the induced emf?
25. With problem 24 (worked out in class) in mind, what is the power supplied to the moving wire by the external agency? Show that this power is equal to I**2 x R dissipated in the lamp.
33. A 25-turn coil is made to rotate in an uniform 0.35 T magnetic field. Each turn has two 10-cm wire lengths that cut the field at varying angles as the coil rotates. What is the emf when the wire is moving with a speed of 22m/s at 90 degrees to the field?
39. An air-core coil with 500 turns has an inductance of 200 mH. If a current of 2.0 A passes through the coil, what will be the flux within it at that moment?
45. If an emf of 10 V is induced across a coil when the current within it is changing at a constant rate of 2.0 A/s, what is the inductance?