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# hw3 - Section 34-4 Electromagnetic Waves Problem 7 At a...

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Section 34-4: Electromagnetic Waves Problem 7. At a particular point the instantaneous electric field of an electromagnetic wave points in the +y direction, while the magnetic field points in the -z direction. In what direction is the wave propagating? Solution For electromagnetic waves in vacuum, the directions of the electric and magnetic fields, and of wave propagation, form a right-handed coordinate system, as shown. (The vector relationship is summarized in Equation 3420b.) Therefore, the given wave is headed in the -x-direction. Problem 7 Solution. Problem 9. The electric field of a radio wave is given by E = Esin(kz - wt)(T + j). (a) What is the peak amplitude of the electric field? (b) Give a unit vector in the direction of the magnetic field at a place and time where sin(kz - wt) is positive. Solution (a) The peak amplitude is the magnitude of E ( i + j), which is ~ 4 . Note that i+ j= d f i , where h is a unit vector 45" between the positive x and y axes. (b) When E is parallel to h (for sin(kz - wt) positive) B points 43" into the second quadrant (so that E I B , and E x B is in the +z direction). Thus, B is parallel to the unit vector (-i + j ) / d . Problem 13. Your intercontinental telephone call is carried by electromagnetic waves routed via a satellite in geosynchronous orbit at an altitude of 36,000 km.

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