29 HMK #7 Chp 29b

29 HMK #7 Chp 29b - Ch. 29 PHYSICS 2B Spring 2011 Homework...

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Ch. 29 PHYSICS 2B Spring 2011 Homework Solutions – Chapter 29 Author: Evan Grohs - egrohs@physics.ucsd.edu Ch. 29 Problems: 1, 4, 6, 14, 15, 18, 20, 22, 24, 27, 35, 49, 55, 64, 71 Page 1/8
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Ch. 29 page 2/8 E LECTROMAGNETIC I NDUCTION Note: There is a typesetting error in the solution to problem 29.71. B d d dt ) ± El = & & ² ú should be: i.e. one of the statements of Faraday’s Law. 29.1. I DENTIFY : The changing magnetic field causes a changing magnetic flux through the loop. This induces an emf in the loop which causes a current to flow in it. S ET U P : H ') B ' t , ) B BA cos I , 0 q . A is constant and B is changing. E XECUTE : (a) A ' B ' t 0 . 0900 m 2 ³´ 0 . 190 T/s 0 . 0171 V . ( b ) E VALUATE : These are small emfs and currents by everyday standards. 29.4. I DENTIFY and S ET U P : Apply the result derived in Exercise 29.3: /. QN B AR In the present exercise the flux changes from its maximum value of B BA ) to zero, so this equation applies. R is the total resistance so here 60.0 45.0 105.0 . R : : E XECUTE : 5 42 (3.56 10 C)(105.0 ) says 0.0973 T. 120(3.20 10 m ) NBA QR QB RN A ± ± u: u E VALUATE : A field of this magnitude is easily produced. 29.6. I DENTIFY : Apply Eq.(29.4). IR E S ET U P : // . B dd t A d B d t E XECUTE : (a) 54 4 () ( 0 . 0 1 2 T / s ) ( 3 . 0 01 0 T / s) B Nd d d N ABN A t t dt dt dt ± ) µ u E ³ ´ 44 3 43 3 (0.012 T/s) (1.2 10 T/s ) 0.0302 V (3.02 10 V/s ) . N At t ±± µ u µ u E (b) At 5.00 s, t 3 0.0302 V (3.02 10 V/s )(5.00 s) 0.0680 V. ± µ u E 4 0.0680 V 1.13 10 A. 600 I R ± u : E E VALUATE : The rate of change of the flux is increasing in time, so the induced current is not constant but rather increases in time. 29.14. I DENTIFY : A change in magnetic flux through a coil induces an emf in the coil. 29
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Ch. 29 page 3/8 S ET U P : The flux through a coil is ) = NBA cos I and the induced emf is /. dd t ) E E XECUTE : The flux is constant in each case, so the induced emf is zero in all cases. E VALUATE : Even though the coil is moving within the magnetic field and has flux through it, this flux is not changing , so no emf is induced in the coil. 29.15. I DENTIFY and S ET U P : The field of the induced current is directed to oppose the change in flux. E XECUTE : (a) The field is into the page and is increasing so the flux is increasing. The field of the induced current is out of the page. To produce field out of the page the induced current is counterclockwise. (b) The field is into the page and is decreasing so the flux is decreasing. The field of the induced current is into the page. To produce field into the page the induced current is clockwise. (c) The field is constant so the flux is constant and there is no induced emf and no induced current. E VALUATE : The direction of the induced current depends on the direction of the external magnetic field and whether the flux due to this field is increasing or decreasing. 29.18. I DENTIFY : Apply Lenz’s law. S ET U P : The field of the induced current is directed to oppose the change in flux in the primary circuit.
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29 HMK #7 Chp 29b - Ch. 29 PHYSICS 2B Spring 2011 Homework...

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