32 HMK #8 Chp 30

32 HMK #8 Chp 30 - Ch. 30 PHYSICS 2B Spring 2011 Homework...

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Ch. 30 PHYSICS 2B Spring 2011 Homework Solutions – Chapter 30 Author: Evan Grohs - [email protected] Ch. 30 Problems: 1, 5, 8, 19, 24, 27, 33, 36, 50, 66, 68 Page 1/6
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Ch. 30 page 2/6 I NDUCTANCE 30.1. I DENTIFY and S ET U P : Apply Eq.(30.4). E XECUTE : (a) 4 1 2 (3.25 10 H)(830 A/s) 0.270 V; di M dt  E yes, it is constant. (b) 2 1 ; di M dt E M is a property of the pair of coils so is the same as in part (a). Thus 1 0.270 V. E E VALUATE : The induced emf is the same in either case. A constant / di dt produces a constant emf. 30.5. I DENTIFY and S ET U P : Apply Eq.(30.5). E XECUTE : (a)   22 1 400 0.0320 Wb 1.96 H 6.52 A B N M i (b) 3 11 2 1 21 (1.96 H)(2.54 A) so 7.11 10 Wb 700 B B NM i M iN  E VALUATE : M relates the current in one coil to the flux through the other coil. Eq.(30.5) shows that M is the same for a pair of coils, no matter which one has the current and which one has the flux. 30.8. I DENTIFY : A changing current in an inductor induces an emf in it. (a) S ET U P : The self-inductance of a toroidal solenoid is 2 0 . 2 N A L r E XECUTE : 72 4 2 4 (4 10 T m/A)(500) (6.25 10 m ) 7.81 10 H 2 (0.0400 m) L   (b) S ET U P : The magnitude of the induced emf is . di L dt E E XECUTE :  4 3 5.00 A 2.00 A 0.781 V 3.00 10 s     E (c) The current is decreasing, so the induced emf will be in the same direction as the current, which is from a to b, making b at a higher potential than a. E VALUATE : This is a reasonable value for self-inductance, in the range of a mH. 30.19. I DENTIFY : A current-carrying inductor has a magnetic field inside of itself and hence stores magnetic energy. (a) S ET U P : The magnetic field inside a solenoid is 0 . B nI E XECUTE : 7 (4 10 T m/A)(400)(80.0 A) = 0.161 T 0.250 m B (b) S ET U P : The energy density in a magnetic field is 2 0 . 2 B u 30
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Ch. 30 page 3/6 E XECUTE : 2 43 7 (0.161 T) 1.03 10 J/m 2(4 10 T m/A) u   (c) S ET U P : The total stored energy is U = uV .
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This note was uploaded on 12/18/2011 for the course PHYS 2B 2b taught by Professor Hirsch during the Spring '10 term at UCSD.

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32 HMK #8 Chp 30 - Ch. 30 PHYSICS 2B Spring 2011 Homework...

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