Questions 2, 5, 7, 9, 12, 14, 15
Problems: 1, 3, 6, 7, 17, 20
Q2 A loop of wire is placed in a uniform magnetic field. For whast orientation of the loop is the magnetic flux a maximum? For what orientation is the flux zero?
Q5 The bar is Figure 31.24 moves on rails to the right with a velocity v, and the uniform, constant magnetic field is directed out of the page. Why is the induced current clockwise? If the bar were moving to the left, what wold be the direction of the induced current?
Q7 A large circular loop of wire lies in the horizontal plane. A bar magnet is dropped through the loop. If the axis of the magnet remains horizontal as it falls, describe the emf induced in the loop. How is the istuation altered if the axis of the magnet remains vertical as it falls?
Q9 Will dropping a magnet down a long copper tube produce a current in the tube?
Q12 What happens when the speed at which the coil of a generator is rotated is increased?
Q14 When the switch in Figure 31.25a is closed, a current is set up in the coil and the metal ring spring upward as in Figure 31.25b. Why?
Q15 Assume the battery in Figure 31.25a is replaced by an ac source and the switch is held closed. If held down, the metal ring on top of the solenoid becomes hot. Why?1
31.1 A 50-turn rectangular coil of dimensions 5.0 cm x 10.0 cm is dropped from a position where B = 0 to a new position where B = 0.50 T and is directed perpendicular to the plane of the coil. Calculate the resulting average emf induced in the coil if the displacement occurs in 0.25 s.
31.3 A powerful electromagnet has a field of 1.6 T and a cross-sectional area of 0.20 m2. If we place a coil having 200 turns and a total resistance of 20 ohms around the electromagnet and then turn off the power to the electromagnet is 20 ms (0.020 s), what is the current induced in the coil?
31.6 A tightly wound circular coil has 50 turns, each of radius 0.10 m. A uniform magnetic field is turned on along a direction perpendicular to the plane of the coils. If the field increases linearly from 0 T to 0.6 T in 0.20 s, what emf is induced in the coil?
31.7 A 30-turn circular coil of radius 4 cm and resistance 1 ohm is placed in a magnetic field directed perpendicularly to the plane of the coil. The magnitude of the magnetic field varies in time according to the expression B = 0.010 t + 0.040 t2, where t is in seconds and B is in tesla. Calculated the induced emf in the coil at t = 5.0 s.
31.17 A Boeing 747 jet with a wing span of 60.0 m is flying horizontally at a speed of 300 m/s over Phoenix where the direction of Earth's magnetic field is 58o below the horizontal. If the magnetiude of the magentic field is 50.0 microTeslas, what is the voltage generateded between the wing tips?
31.20 In Figure P31.20, the bar magnet is moved toward the loop. Is Va - Vb positive, negative, or zero?
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(c) Doug Davis, 2002; all rights reserved