Mid-Term_Exam_Solutions_Spring2011

Mid-Term_Exam_Solutions_Spring2011 - Mid-Term Exam Graduate...

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Mid-Term Exam: Graduate Electromagnetics II, 95.658 Spring 2011, UMass Lowell, Dr. Baird Part I: Multiple Choice (60 Points) Circle the one best answer to each question. 1. What is the wave E = E 0 sin( kx )e - t/τ e -i ωt ? (a) a traveling wave decaying in time (b) a traveling wave packet (c) a standing wave decaying in time (d) a traveling wave decaying in space 2. What does “normal dispersion” describe? (a) lower frequencies are absorbed more strongly (b) higher frequencies are absorbed more strongly (c) lower frequencies are refracted more strongly (d) higher frequencies are refracted more strongly 3. Which is not a valid description of a circularly polarized plane wave? (a) a wave where the electric field vector's magnitude remains constant (b) two linearly polarized waves that are orthogonal and out of phase by 90° (c) two linearly polarized waves that are orthogonal and in phase (d) a wave where the tip of the electric field vector sweeps out a circular spiral in space 4. What is the phase difference between the magnetic field and the electric field in a radiated wave? (a) it depends on the source's multipole moments (b) it depends on the frequency (c) zero (d) π 5. When might the electric field and magnetic field in a wave not be perpendicular to k ? (a) in a waveguide (b) in free space (c) they are always perpendicular to k (d) they are never perpendicular to k 6. Where might we find a wave E = E 0 e - αx e -i ωt , (here E 0 does not depend on x or t , but may depend on other things, and α is a non-zero real number)? (a) in a waveguide below the cutoff frequency (b) in a pure plasma below the plasma frequency (c) as the transmitted wave during total internal reflection (d) all of the above 7. What happens to traveling waves incident on a plasma above the plasma frequency? (a) they are transmitted (b) they are strongly reflected (c) they are completely absorbed (d) they are frozen
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8. What can cause the intensity of electromagnetic waves traveling in materials to decay spatially? (a) damping of electron oscillations due to collisions (b) a non-zero imaginary part of the permittivity (c) a non-zero imaginary part of the wave number k (d) all of the above – they are all connected 9. In what direction do evanescent waves carry energy?
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This note was uploaded on 02/13/2012 for the course PHYSICS 95.658 taught by Professor Staff during the Spring '11 term at UMass Lowell.

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Mid-Term_Exam_Solutions_Spring2011 - Mid-Term Exam Graduate...

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