# hw11sols - MasteringPhysics 2:21 AM Assignment Display Mode...

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4/21/08 2:21 AM MasteringPhysics Page 1 of 10 http://session.masteringphysics.com/myct Assignment Display Mode: View Printable Answers Physics 202 Assignment 11 Due at 11:00pm on Wednesday, April 16, 2008 View Grading Details Electric and Magnetic Field Vectors Conceptual Question Description: Short conceptual questions about the direction the electromagnetic wave, electric field, and magnetic field vectors point. Part A The electric and magnetic field vectors at a specific point in space and time are illustrated. Based on this information, in what direction does the electromagnetic wave propagate? Hint A.1 Right-hand rule for electromagnetic wave velocity In an electromagnetic wave, the electric and magnetic field vectors are perpendicular to each other. The wave propagates in a direction perpendicular to both of the field vectors. Since the two field vectors define a two-dimensional plane, there are two distinct directions that are perpendicular to the plane. The right-hand rule specifies in which of these two directions the wave travels. To employ the right hand rule, do the following: 1. Point the fingers of your right hand in the direction of the electric field vector. 2. Rotate your hand until you can curl your fingers in the direction of the magnetic field vector. The direction of your thumb is then the direction of the velocity of the electromagnetic wave. If the electric and magnetic field vectors at a specific point in space and time are as shown below, applying the right- hand rule should result in your thumb pointing downward, in the – y direction. Therefore, the velocity of the electromagnetic wave is in the – y direction. ANSWER: + x x + y y + z z at a +45 angle in the xy plane Part B The electric and magnetic field vectors at a specific point in space and time are illustrated. ( and are in the xy plane. Both vectors make 45 angles with the y axis.) Based on this information, in what direction does the electromagnetic wave propagate?

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4/21/08 2:21 AM MasteringPhysics Page 2 of 10 http://session.masteringphysics.com/myct ANSWER: + x x + y y + z z at a –45 angle in the xy plane Part C The magnetic field vector and the direction of propagation of an electromagnetic wave are illustrated. Based on this information, in what direction does the electric field vector point? Hint C.1 Working backward with the right-hand rule Since the velocity of the wave is given, the orientation of your right thumb is known. Placing your right thumb along the + x axis should inform you that the electric field vector must be in the yz plane. Since the electric field must also be perpendicular to the magnetic field, and be "curlable" into the magnetic field, only one option remains for the orientation of the electric field vector.
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