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su10EIIIS - Physics 54 Summer 2010 Exam III Solutions Part...

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Exam III Solutions Part A. Multiple choice questions. Check the best answer. Each question carries a value of 4 points. 1. A radio is being tuned to a local station. At first there is no discernible signal from the antenna. Then the capacitance of the tuning circuit (a series LCR circuit with the antenna as emf) is increased slightly and the local station’s signal is received clearly. Which of the following is wrong? The station’s frequency is higher than the one originally tuned to. [Lower.] The same result would have occurred if the inductance had been increased instead of the capacitance. Before the capacitance was changed, the rms voltage across the capacitor was greater than across the inductor. One of the above is wrong. 2. At a given place and time the E-field of a light wave is in the + y -direction and its B-field is in the + x -direction. The wave is propagating in the + z -direction. [- z .] If a polaroid filter with transmission axis in the y -direction is placed in the path of the wave, the wave’s energy will be absorbed by the filter. [Transmitted.] A possible formula for the E-field is E = E 0 cos( kz + ω t ) j . The E and B fields have the same amplitude. [ E = cB .] Physics 54 Summer 2010 1
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3. Unpolarized light is incident at angle θ 1 from a medium with refractive index n 1 onto the interface with a medium of refractive index n 2 . The light is totally reflected. Which of the following is wrong? If θ 1 < 90 ° then n 2 < n 1 . If n 2 > n 1 then θ 1 = 90 ° . The reflected light is partially polarized with E perpendicular to the plane of incidence. [Remains unpolarized.] If n 2 < n 1 then θ 1 is greater than the critical angle. [Or equal.] 4. Concerning defects of vision, which of the following is wrong? For a person whose far point is 20 m, the corrective lens has focal length –20 m.
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