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sol-e3-sm09

# sol-e3-sm09 - Phy 2049 Exam III Solutions 1 A ray of light...

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Phy 2049 Exam III Solutions July 20, 2009 1. A ray of light from medium a, whose index of refraction is 1.89, enters medium b. The angle of incidence θ a is 50 and the angle of refraction θ b is 60 . What is the index of refraction of medium b? (1) 1.7 (2) 1.4 (3) 1.3 (4) 1.2 (5) 1.5 Snell’s law n a sin θ a = n b sin θ b or n b = 1.89 sin50/sin60 = 1.67 2. In the Figure L 1 = 20 mH, L 2 = 30 mH and L 3 = 40 mH. The equivalent inductance (in mH) between the wire ends is: (a) 22 (b) 90 (c) 9.2 (d) 40 (e) 66 Here L 1 and L 2 are in series (equivalent inductance 50mH) and the combination is parallel to L 3 . The final equivalent inductance is L = 50x40/(50+40) = 22mH . 3. The light from a professor’s laser pointer can be considered as an electromagnetic plane wave. If the laser beam has 5 mW of power and illuminates a circular spot 2.5 mm in radius on a screen, what is the maximum electric field amplitude (E m in N/C) at the screen? (1) 440 (2) 311 (3) 622 (4) 550 (5) none of these The intensity of the light is I = 5mW/(π(2.5mm)2) = 255W/m2. It is related to the maximum electric field amplitude via I = E 2 m /(2cμ o ). E m = 438 V/m=N/C. 4. A horizontal beam of unpolarized light is incident upon a stack of 4 polarizers with axes of polarization, in order and measured clockwise from the vertical, at 30 ° , 75°, 120 ° and 180 °, . What is the ratio of the intensity of the transmitted beam to that of the incident beam?

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sol-e3-sm09 - Phy 2049 Exam III Solutions 1 A ray of light...

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