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Unformatted text preview: brown (twb493) ch25-h1 chiu (56565) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A particular AM radio station broadcasts at a frequency of f= 920 kHz. What is the wavelength of this electromagnetic radiation? Remember that c = 3 10 8 m / s . Correct answer: 326 . 087 m. Explanation: Applying = c f , = c f = 3 10 8 m / s 9 . 2 10 5 Hz = 326 . 087 m 002 (part 2 of 2) 10.0 points How much time is required for the radiation to propagate from the broadcasting antenna to a radio d = 13 . 5 km away? Correct answer: 4 . 5 10 5 s. Explanation: Noting that d = c t , t = | vectorr | c t 13500 m 3 10 8 m / s 4 . 5 10 5 s 003 10.0 points Consider the two examples of the cosine curves displayed in the figure below. Study the two curves, and make sure you under- stand the relationship between them. Choose the graph that correctly displays the plot of E cos parenleftbigg 2 t T + parenrightbigg . E cos parenleftbigg 2 t T parenrightbigg E cos parenleftbigg 2 t T + 2 parenrightbigg t =0 T 2 T t t 1. t =0 T 2 T t 2. t =0 T 2 T t 3. t =0 T 2 T t brown (twb493) ch25-h1 chiu (56565) 2 4. t =0 T 2 T t correct Explanation: The graph of E cos parenleftbigg 2 t T + parenrightbigg has a mini- mum value of -E when t takes on values of zero and even multiples of T/2. It has a maximum value of E when t takes on odd multiples of T/2. To be out of phase means that the two graphs reach their maximums and their mini- mums at different times. 004 (part 1 of 7) 10.0 points The height of a particular water wave is de- scribed by the function y = A cos bracketleftbigg B t C x + 2 bracketrightbigg , where A = 0 . 84823 m B = 1 . 69646 s 1 C = 0 . 339292 m 1 . Determine the angular frequency . Correct answer: 1 . 69646 s 1 . Explanation: Note that the general form of this equation is: y = A cos( t kx + ) where k = 2 / is called the wavenumber. (Note that in spectroscopy, wavenumber is defined as 1 / , so chemists generally use this definition of wavenumber.) Based on the general form of the equation, we can see that the angular frequency multi- plies t , so in this case = B = 1 . 69646 s 1 . You could also have deduced this through unit analysis. B is the only number that has the units of frequency. 005 (part 2 of 7) 0.0 points WITHDRAWN 006 (part 3 of 7) 0.0 points WITHDRAWN 007 (part 4 of 7) 10.0 points Determine the wavelength . Correct answer: 18 . 5185 m. Explanation: We know that k must be given by C above, because in the general form of the equation k multiplies x . And since 2 / = k , we have 2 = 0 . 339292 m 1 so, = 18 . 5185 m 008 (part 5 of 7) 0.0 points WITHDRAWN 009 (part 6 of 7) 10.0 points What is the direction of propagation....
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- Fall '08