Chapter 29 - 29 Magnetic Fields CHAPTER OUTLINE 29.1 29.2...

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29 CHAPTER OUTLINE 29.1 Magnetic Fields and Forces 29.2 Magnetic Force Acting on a Current-Carrying Conductor 29.3 Torque on a Current Loop in a Uniform Magnetic Field 29.4 Motion of a Charged Particle in a Uniform Magnetic Field 29.5 Applications Involving Charged Particles Moving in a Magnetic Field 29.6 The Hall Effect Magnetic Fields ANSWERS TO QUESTIONS Q29.1 The force is in the + y direction. No, the proton will not continue with constant velocity, but will move in a circular path in the x-y plane. The magnetic force will always be perpendicular to the magnetic field and also to the velocity of the proton. As the velocity changes direction, the magnetic force on the proton does too. Q29.2 If they are projected in the same direction into the same magnetic field, the charges are of opposite sign. Q29.3 Not necessarily. If the magnetic field is parallel or antiparallel to the velocity of the charged particle, then the particle will experience no magnetic force. Q29.4 One particle veers in a circular path clockwise in the page, while the other veers in a counterclockwise circular path. If the magnetic field is into the page, the electron goes clockwise and the proton counterclockwise. Q29.5 Send the particle through the uniform field and look at its path. If the path of the particle is parabolic, then the field must be electric, as the electric field exerts a constant force on a charged particle. If you shoot a proton through an electric field, it will feel a constant force in the same direction as the electric field—it’s similar to throwing a ball through a gravitational field. If the path of the particle is helical or circular, then the field is magnetic—see Question 29.1. If the path of the particle is straight, then observe the speed of the particle. If the particle accelerates, then the field is electric, as a constant force on a proton with or against its motion will make its speed change. If the speed remains constant, then the field is magnetic—see Question 29.3. Q29.6 Similarities: Both can alter the velocity of a charged particle moving through the field. Both exert forces directly proportional to the charge of the particle feeling the force. Positive and negative charges feel forces in opposite directions. Differences: The direction of the electric force is parallel or antiparallel to the direction of the electric field, but the direction of the magnetic force is perpendicular to the magnetic field and to the velocity of the charged particle. Electric forces can accelerate a charged particle from rest or stop a moving particle, but magnetic forces cannot. 161
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162 Magnetic Fields Q29.7 Since Fv B B q af , then the acceleration produced by a magnetic field on a particle of mass m is av B B q m . For the acceleration to change the speed, a component of the acceleration must be in the direction of the velocity. The cross product tells us that the acceleration must be perpendicular to the velocity, and thus can only change the direction of the velocity.
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This homework help was uploaded on 04/13/2008 for the course PHYS 211 taught by Professor Shannon during the Spring '08 term at MSU Bozeman.

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Chapter 29 - 29 Magnetic Fields CHAPTER OUTLINE 29.1 29.2...

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