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ch25-h1-solutions

# ch25-h1-solutions - pan(zp695 ch25-h1 chiu(56565 This...

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pan (zp695) – 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= 900 kHz. What is the wavelength of this electromagnetic radiation? Remember that c = 3 × 10 8 m / s . Correct answer: 333 . 333 m. Explanation: Applying λ = c f , λ = c f = 3 × 10 8 m / s 9 × 10 5 Hz = 333 . 333 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 = 11 . 5 km away? Correct answer: 3 . 83333 × 10 - 5 s. Explanation: Noting that d = c Δ t , Δ t = | r | c Δ t 11500 m 3 × 10 8 m / s 3 . 83333 × 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 2 π t T + π . E cos 2 π t T E cos 2 π t T + π 2 t =0 T 2 T t t 1. t =0 T 2 T t 2. t =0 T 2 T t correct 3. t =0 T 2 T t

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pan (zp695) – ch25-h1 – chiu – (56565) 2 4. t =0 T 2 T t Explanation: The graph of E cos 2 π t T + π 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 di ff erent 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 B t - C x + π 2 , where A = 1 . 19381 m B = 2 . 38761 s - 1 C = 0 . 477522 m - 1 . Determine the angular frequency ω . Correct answer: 2 . 38761 s - 1 . Explanation: Note that the general form of this equation is: y = A cos( ω t - 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 = 2 . 38761 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: 13 . 1579 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 . 477522 m - 1 so, λ = 13 . 1579 m 008 (part 5 of 7) 0.0 points WITHDRAWN 009 (part 6 of 7) 10.0 points What is the direction of propagation. 1. +x direction correct 2. Neither 3. - x direction Explanation: The direction of propogation is +x direc- tion because the sign in ( ω t - kx ) is negative. 010 (part 7 of 7) 10.0 points At ( x, t ) = (0 , 0), what is the amplitude of the wave? Correct answer: 0 m. Explanation: At ( x, t ) = (0 , 0), y = Acos π 2 . Thus, the height of the wave at x = 0 and t = 0 is zero.
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ch25-h1-solutions - pan(zp695 ch25-h1 chiu(56565 This...

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