Exam__2_11_1_07_Solutions

# Exam__2_11_1_07_Solutions - PHYSICS 222, FALL 2007 EXAM #2...

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PHYSICS 222, FALL 2007 EXAM #2 SOLUTIONS NOVEMBER 1, 2007 Problems 31-45 are worth 2 points each. 31. The displacement wave in a traveling sinusoidal sound wave moving along the x-axis in a gas has the wave function y(x,t) = A sin(kx ω t). The amplitude of the pressure wave in the sound wave is ____ . (B is the bulk modulus of the gas) A. BA B. BA/k C. Ak D. Ak/B E. BAk p(x,t) = B y(x,t) x = B A sin(kx ω t) x = kAB cos(kx ω t), so p max = BAk . 32. The pressure wave in the third harmonic standing sound wave in the gas in a pipe with one end open and one end closed has _____ nodes. A. 1 B. 2 C. 3 D. 4 E. 5 The third harmonic standing wave has 3/4 of a wavelength of both the displacement wave and the pressure wave in it. Each type of wave has two nodes and two antinodes. 33. The magnetic field wave in a plane electromagnetic traveling wave in vacuum has the wave function B (z, t) = B max sin(kz + ω t) j ˆ . The electomagnetic wave is moving in the ____ direction. A. k ˆ B. i ˆ C. k ˆ D. j ˆ E. i ˆ As in any sinusoidal traveling wave, the phase of the sine function, (kz + ω t), tells us that the wave is moving in the k ˆ direction. 34. Maxwell's equations for electric and magnetic fields in vacuum are: (1) O E · d A = 0 (3) O B · d l = µ o ε o d Φ E dt (2) O B · d A = 0 (4) O E d l = d Φ B dt Which two of these equations can be used to derive the existence and speed of electromagnetic traveling plane waves in vacuum? A. (1) and (2) B. (2) and (3) C. (3) and (4) D. (1) and (3) E. (2) and (4)

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35. The electric and magnetic fields in a traveling plane electromagnetic wave in vacuum at a particular point in space and at a particular instant of time are E and B , respectively. The direction of propagation of the wave is in the direction of ____ . A. E B. B C. B × E D. E × B E. E · B 36. A block of glass has an index of refraction of 1.50. The speed of light in the glass is ____, where c is the speed of light in vacuum. A. (1/3) c B. (1/2) c C. (2/3) c D. c E. (3/2) c v = c n = c 3/2 = (2/3) c . 37. A monochromatic beam of light is incident from transparent medium 1 with index of refraction n 1 onto a flat interface with transparent medium 2 with index of refraction n 2 . Which one of the following five statements is true? A. The reflection of light from the interface is called diffuse reflection. B. In order for it to be possible for total internal reflection to occur at the interface, n 1 must be less than n 2 . C. The angle of refraction is smaller than the angle of incidence if n 1 is larger than n 2 . D. The frequency of the light is the same in both media.
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## This note was uploaded on 02/11/2012 for the course PHYSICS 222 taught by Professor Ogilvie during the Fall '05 term at Iowa State.

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Exam__2_11_1_07_Solutions - PHYSICS 222, FALL 2007 EXAM #2...

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