27 - MasteringPhysics: Assignment Print View

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MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrint?assig. .. 1 of 13 17/4/07 16:06 [ Assignment View ] E ð lisfræ ð i 2, vor 2007 27. Magnetic Field and Magnetic Forces Assignment is due at 2:00am on Wednesday, February 28, 2007 Credit for problems submitted late will decrease to 0% after the deadline has passed. The wrong answer penalty is 2% per part. Multiple choice questions are penalized as described in the online help. The unopened hint bonus is 2% per part. You are allowed 4 attempts per answer. Forces on moving charges and currents in Magnetic Field Force on Moving Charges in a Magnetic Field Learning Goal: To understand the force on a charge moving in a magnetic field. Magnets exert forces on other magnets even though they are separated by some distance. Usually the force on a magnet (or piece of magnetized matter) is pictured as the interaction of that magnet with the magnetic field at its location (the field being generated by other magnets or currents). More fundamentally, the force arises from the interaction of individual moving charges within a magnet with the local magnetic field. This force is written , where is the force, is the individual charge (which can be negative), is its velocity, and is the local magnetic field. This force is nonintuitive, as it involves the vector product (or cross product) of the vectors and . In the following questions we assume that the coordinate system being used has the conventional arrangement of the axes, such that it satisfies , where , , and are the unit vectors along the respective axes. Let's go through the right-hand rule. Starting with the generic vector cross-product equation point your forefinger of your right hand in the direction of , and point your middle finger in the direction of . Your thumb will then be pointing in the direction of . Part A Consider the specific example of a positive charge moving in the + x direction with the local magnetic field in the + y direction. In which direction is the magnetic force acting on the particle? Express your answer using unit vectors (e.g., - ). (Recall that is written x_unit .) ANSWER: Direction of = Part B Now consider the example of a positive charge moving in the + x direction with the local magnetic field in the + z direction. In which direction is the magnetic force acting on the particle? Express your answer using unit vectors. ANSWER: Direction of = Part C [
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MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrint?assig. .. 2 of 13 17/4/07 16:06 Now consider the example of a positive charge moving in the xy plane with velocity (i.e., with magnitude at angle with respect to the x axis). If the local magnetic field is in the + z direction, what is the direction of the magnetic force acting on the particle? Hint C.1 Finding the cross product
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27 - MasteringPhysics: Assignment Print View

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