QuestionsCh27

QuestionsCh27 - CHAPTER 27: Magnetism Responses to...

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CHAPTER 27: Magnetism Responses to Questions 1. The compass needle aligns itself with the local magnetic field of the Earth, and the Earth’s magnetic field lines are not always parallel to the surface of the Earth. 2. The magnetic field lines are concentric circles around the wire. With the current running to the left, the field is directed counterclockwise when looking from the left end. So, the field goes into the page above the wire and comes out of the page below the wire. I 3. The force is downward. The field lines point from the north pole to the south pole, or left to right. Use the right hand rule. Your fingers point in the direction of the current (away from you). Curl them in the direction of the field (to the right). Your thumb points in the direction of the force (downward). 4. F r is always perpendicular to both B r and l r . B r and l r can be at any angle with respect to each other. 5. Alternating currents will have little effect on the compass needle, due to the rapid change of the direction of the current and of the magnetic field surrounding it. Direct currents will deflect a compass needle. The deflection depends on the magnitude and direction of the current and the distance from the current to the compass. The effect on the compass decreases with increasing distance from the wire. 6. The kinetic energy of the particle will stay the same. The magnetic force on the particle will be perpendicular to the particle’s velocity vector and so will do no work on the particle. The force will change the direction of the particle’s velocity but not the speed. Positive particle in the upper left: force is downward toward the wire. Negative particle in the upper right: force is to the left. Positive particle in the lower right: force is to the left.
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This note was uploaded on 03/22/2009 for the course PHY 54L taught by Professor Thomas during the Spring '09 term at Duke.

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QuestionsCh27 - CHAPTER 27: Magnetism Responses to...

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