HW08_Solutions

HW08_Solutions - HOMEWORK 8: SOLUTIONS Q29.13: ANSWER: When...

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HOMEWORK 8: SOLUTIONS Q29.13: ANSWER: When radius of the ring is doubled, its circumference is also doubled, but the area increases four fold. Therefore, a) induced emf will increase 4 fold. b) electric field is emf/length, so it will be doubled. 29.10. I DENTIFY : A change in magnetic flux through a coil induces an emf in the coil. S ET U P : The flux through a coil is Φ = NBA cos φ and the induced emf is E XECUTE : (a) and (c) The magnetic flux is constant, so the induced emf is zero. (b) The area inside the field is changing. If we let x be the length (along the 30.0-cm side) in the field, then A = (0.400 m) x . Φ B = BA = (0.400 m) x = d Φ / dt = B d [(0.400 m) x ]/ dt = B (0.400 m) dx / dt = B (0.400 m) v = (1.25 T)(0.400 m)(0.0200 m/s) = 0.0100 V E VALUATE : It is not a large flux that induces an emf, but rather a large rate of change of the flux. The induced emf in part (b) is small enough to be ignored in many instances. 29.21. I DENTIFY : A conductor moving in a magnetic field may have a potential difference induced across it, depending on how it is moving. S ET U P : The induced emf is = vBL sin , where is the angle between the velocity and the magnetic field. E XECUTE : (a) = vBL sin = (5.00 m/s)(0.450 T)(0.300 m)(sin 90°) = 0.675 V (b) The positive charges are moved to end b , so b is at the higher potential. (c) E = V/L = (0.675 V)/(0.300 m) = 2.25 V/m. The direction of is from, b to a . (d) The positive charge are pushed to b , so b has an excess of positive charge. (e) (i) If the rod has no appreciable thickness, L = 0, so the emf is zero. (ii) The emf is zero because no magnetic force acts on the charges in the rod since it moves parallel to the magnetic field. E VALUATE : The motional emf is large enough to have noticeable effects in some cases. 29.29.

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This note was uploaded on 02/11/2012 for the course PHYSICS 222 taught by Professor Ogilvie during the Fall '05 term at Iowa State.

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HW08_Solutions - HOMEWORK 8: SOLUTIONS Q29.13: ANSWER: When...

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