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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 two-lens 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 z-axis from positive z and looking toward the origin, is a (B) line at 135 ◦ to the + x-axis 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
- Diffraction, Magnetic Field, Wavelength