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Unformatted text preview: brown (twb493) – ch25h1 – chiu – (56565) 1 This printout should have 27 questions. Multiplechoice 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 λ = c f , λ = 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 = cΔ t , Δ t =  vectorr  c Δ 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 πt T + π parenrightbigg . E cos parenleftbigg 2 π t T parenrightbigg E cos parenleftbigg 2 π t T + π 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) – ch25h1 – chiu – (56565) 2 4. t =0 T 2 T t correct Explanation: The graph of E cos parenleftbigg 2 π t T + π 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 + π 2 bracketrightbigg , where A = 0 . 84823 m B = 1 . 69646 s − 1 C = 0 . 339292 m − 1 . Determine the angular frequency ω . Correct answer: 1 . 69646 s − 1 . Explanation: Note that the general form of this equation is: y = A cos( ωt − kx + φ ) where k = 2 π/λ is called the wavenumber. (Note that in spectroscopy, wavenumber is defined as 1 /λ , 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 ω = 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 λ . 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 π/λ = k , we have 2 π λ = 0 . 339292 m − 1 so, λ = 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
 Turner
 Physics, Light, ch25h1 – chiu

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