* he electromotive force induced in the inductor is 10 mV, what is it self-induction coefficient of such coil? a. 6.25 x104 H. b. 6.25 x10-3 H. c. 7.5x104 H. d. 7.5x10-3 H. 10. The forward induced e.m.f by mutual induction in a secondary coil is produced by all the following except.. a. Switching off the primary current. b. Switching on the primary current. c. Increasing the resistance of the rheostat in the primary circuit. d. Increasing the distance between the primary and the secondary coil. 11. The mutual inductance is measured in all the following units except. . b. 2.s C. volt.A1.s. d. Henry. a. Volt.A.s! 12. Doubling the number of turns for a solenoid at constant of other factors, its

* he electromotive force induced in the inductor is 10 mV, what is it self-induction coefficient of such coil? a. 6.25 x104 H. b. 6.25 x10-3 H. c. 7.5x104 H. d. 7.5x10-3 H. 10. The forward induced e.m.f by mutual induction in a secondary coil is produced by all the following except.. a. Switching off the primary current. b. Switching on the primary current. c. Increasing the resistance of the rheostat in the primary circuit. d. Increasing the distance between the primary and the secondary coil. 11. The mutual inductance is measured in all the following units except. . b. 2.s C. volt.A1.s. d. Henry. a. Volt.A.s! 12. Doubling the number of turns for a solenoid at constant of other factors, its

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter15: Alternating-current Circuits

Section: Chapter Questions

Problem 48P: A transformer is used to supply a 12-V model train with power from a 110-V wall plug. The train...

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Two rectangular loops of wire lie in the same plane as shown in Figure OQ31.11. If the current I in the outer loop is counterclockwise and increases with time, what is true of the current induced in the inner loop? More than one statement may be correct, (a) It is zero, (b) It is clockwise, (c) It is counterclockwise, (d) Its magnitude depends on the dimensions of the loops, (e) Its direction depends on the dimensions of the loops.
When a wire carries an AC current with a known frequency, you can use a Rogowski coil to determine the amplitude Imax of the current without disconnecting the wire to shunt the current through a meter. The Rogowski coil, shown in Figure P30.8, simply clips around the wire. It consists of a toroidal conductor wrapped around a circular return cord. Let n represent the number of turns in the toroid per unit distance along it. Let A represent the cross-sectional area of the toroid. Let I(t) = Imax sin t represent the current to be measured. (a) Show that the amplitude of the emf induced in the Rogowski coil is Emax=0nAImax. (b) Explain why the wire carrying the unknown current need not be at the center of the Rogowski coil and why the coil will not respond to nearby currents that it does not enclose. Figure P30.8
Unreasonable Results The 335 kV AC electricity from a power transmission line is fed into the primary coil of a transformer. The ratio of the number of turns in the secondary to the number in the primary is Ns/Np = 1000. (a) What voltage is induced in the secondary? (b) What is unreasonable about this result? (c) Which assumption or premise is responsible?
Eddy current are induced currents set up in a piece of metal when it moves through a nonuniform magnetic field. For example, consider the flat metal plate swinging at the end of a bar as a pendulum, as shown in Figure CQ20.9. (a) At position 1, the pendulum is moving from a region where there is no magnetic field into a region where the field B is directed into the paper. Show that at position 1 the direction of the eddy current is counterclockwise. (b) At position 2, the pendulum is moving out of the field into a region of zero field. Show that the direction of the eddy current is clockwise in this case. (c) Use right-hand rule number 2 to show that these eddy currents lead to a magnetic force on the plate directed at shown in the figure. Because the induced eddy current always produces a retarding force when the plate enters or leaves the field, the swinging plate quickly comes to rest. Figure CQ20.9
A 75-turn, 10.0 cm diameter coil rotates at an angular velocity of 8.00 radius in a 1.25 T field, starting with the plane of the coil parallel to the field. (a) What is the peak emf? (b) At what time is the peak emf first reached? (c) At what time is the emf first at its meet negative? (d) What is the period of the AC voltage output?
A transformer is used to supply a 12-V model train with power from a 110-V wall plug. The train operates at 50 W of power, (a) What is the rms current in the secondary coil of the transformer? (b) What is me rms current in the primary coil? (c) What is the ratio of the number of primary to secondary turns? (d) What is the resistance of the tram? (e) What is the resistance seen by the 110-V source?
A 120-V, series-wound dc motor draws 0.50 A from its power source when operating at full speed, and it draws 2.0 A when it starts. The resistance of the armature coils is 10 , (a) What is the resistance of the field coils? (b) What is tire back emf of the motor when it is running at full speed? (c) The motor operates at a different speed and draws 1.0 A from the source. What is the back emf in this case?
A large research solenoid has a self-inductance of 25.0 H. (a) What induced emf opposes shutting it off when 100 A of current through it is switched off in 80.0 ms? (b) How much energy is stored in the inductor at full current? (c) At what rate in waits must energy be dissipated to switch the current off in 80.0 ms? (d) In View of the answer to the last part, is it surprising that shutting it down this quickly is difficult?
Referring to Figure 23.57(b), what is the direction of the current induced in the coil: (a) If the current in the wire increases? (b) If the current in fine wire decreases? (c) If the current in the wire suddenly changes direction? Explicitly show how you follow the steps in the Problem-Solving Strategy for Lenz’s Law.
An N-turn circular wire coil of radius r lies in the xy-plane (the plane of the page), as in Figure P20.10. A uniform magnetic field is turned on, increasing steadily from 0 to B0 in the positive z-direction in t seconds. (a) Find a symbolic expression for the emf, , induced in the coil in terms of the variables given. (b) looking down on at the xy-plane from the positive z-axis, is the direction of the induced current clockwise or counterclockwise? (c) If each loop has resistance R, find an expression for the magnitude of the induced current, I.
(a) A car generator turns at 400 rpm when 1he engine is idling. Its 300-turn, 5.00 by 8.00 cm rectangular coil rotates in an adjustable magnetic field 50 that it can produce suf?cient voltage even at low rpms. What is the field strength needed to produce a 24.0 V peak emf? (b) Discuss how this required field strength compares to those available in permanent and electromagnets.
The open switch in Figure CQ32.7 is thrown closed at t = 0. Before the switch is closed, the capacitor is uncharged and all currents are zero. Determine the currents in L, C. and R, the emf across L, and the potential differences across C and R (a) at the instant after the switch is closed and (b) long after it is closed.