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Unformatted text preview: Ph 214, Spring 2007 Exam # 1 Multiple Choice Name: (no name, no score !) 1. [5 pts] An object is located 40 centimeters to the left of the first of two thin converging lenses of focal lengths +20 centimeters and +10 centimeters, respectively, as shown in the figure below. The lenses are separated by 30 centimeters. The final image formed by the twolens system is located (A) 5.0 cm to the right of the second lens 2. [5 pts] An electromagnetic plane wave, propagating in vacuum, has an electric field given by E = E cos( kx ωt ) and is normally incident on a perfect conductor at x = 0, as shown in the figure below. Immediately to the left of the conductor, the total electric field E and the total magnetic field B are given by which of the following? ( Hint: think about the boundary conditions. ) E B (C) (2 E /c ) cos ωt For Questions 3 & 4: Consider a plane electromagnetic wave that is a superposition of two independent orthogonal plane waves and can be written as E = E 1 cos( kz ωt ) ˆ x + E 2 cos( kz ωt + π ) ˆ y . 3. [5 pts] For E 1 = E 2 , the tip of the electric field vector will describe a trajectory that, as viewed along the zaxis from positive z and looking toward the origin, is a (B) line at 135 ◦ to the + xaxis 4. [5 pts] If the original plane wave is split and recombined on a screen after the two portions, E 1 cos( kz ωt ) ˆ x & E 2 cos( kz ωt + π ) ˆ y , have traveled an optical path difference of 2 π/k , the observed average intensity will be proportional to (A) E 2 1 + E 2 2 5. [5 pts] Just after sunrise, sunlight scattered from molecules (primarily O 2 and N 2 ) in the atmosphere directly overhead is strongly polarized. Assuming that the the light from the Sun is coming from a direction exactly...
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 Spring '08
 Faculty
 Diffraction, Magnetic Field, Wavelength

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