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Quiz09_solutions - Physics 222 Name Section Quiz 9A An...

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Physics 222 Fall 2011 Name:_______________ Section:______________ Quiz 9A An electromagnetic wave in vacuum is moving in the positive z direction. a. At a particular time t and at a particular position, the electric field component of this wave is 10.0 V/m and is pointing in the positive y direction. In what direction is the magnetic field component pointing at that time and position? What is the magnitude of this magnetic field? Solution: Wave velocity is in the same direction as E × B . From the right-hand rule followes that B is directed the negative x direction. E is related to B by E = cB , so B = E/c = (10.0 V/m)/(3.00×10 8 m/s) = 33.3 nT. b. If (10.0 V/m) happens to be the maximum magnitude of the wave's electric field, what is the wave's intensity? Solution: Intensity is given by ( 29 ( 29 ( 29 2 2 2 2 -12 8 2 1 2 max 0 2 1 / 133 / 0 . 10 /Nm C 10 85 . 8 m/s 10 3.00 m mW m V E c I = = = ε or equivalently: I = E max 2 /(2 µ 0 c) = (10.0 V/m) 2 /[2(4π×10 -7 m×T/A)(3.00×10 8 m/s)]= 133 mW/m 2 .
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Physics 222 Fall 2011 Name:_______________ Section:______________ Quiz 9B An electromagnetic wave is moving in vacuum.
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