# panda 1 - pokharel(pp7242 Electromagnetic Waves...

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pokharel (pp7242) – Electromagnetic Waves – walther – (16180) 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. I am defnitely not , For no way , am not going to extended the dateline on this. 001 10.0 points A radar operates at a wavelength oF 3 cen- timeters. The speed oF light is 3 × 10 8 m / s. What is the Frequency oF the these waves? 1. f = 10 10 Hz correct 2. f = 3 × 10 8 Hz 3. f = 10 - 10 Hz 4. f = 10 8 Hz 5. f = 10 6 Hz Explanation: Let : λ = 3 cm = 0 . 03 m and c = 3 × 10 8 . The Frequency is f = c λ = 3 × 10 8 m / s 0 . 03 m = 1 × 10 10 Hz . 002 10.0 points A radar operates at a wavelength oF 7 . 8 cm. What is the Frequency oF the these waves in Hz? Correct answer: 3 . 84615 × 10 9 Hz. Explanation: Let : λ = 7 . 8 cm = 0 . 078 m and c = 3 × 10 8 m / s . The Frequency is thus f = c λ = 3 × 10 8 m / s 0 . 078 m = 3 . 84615 × 10 9 Hz . 003 10.0 points The intensity oF light From a central source varies inversely as the square oF the distance. IF you lived on a planet only halF as Far From the Sun as our Earth, how would the intensity compare with that on Earth? 1. Two times 2. ±our times correct 3. Eight times 4. Three times Explanation: Light intensity obeys the inverse square I 1 r 2 . Thus I 1 p 1 2 r P 2 = 1 1 4 r 2 = 4 · 1 r 2 , and For the planet halF as Far From the sun, light would be Four times as intense. 004 10.0 points Suppose a sound wave and an electromagnetic wave have the same Frequency. Which has the longer wavelength? 1. the sound wave 2. the electromagnetic wave correct 3. It depends on the speed oF the sound wave. 4. They have the same wavelength. Explanation: The wavelength oF the electromagnetic wave will be much longer because oF its greater speed. You can see this From the equation v = ; For the same Frequency greater speed means greater wavelength. Or you can think oF the Fact that in the time oF one period (the

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pokharel (pp7242) – Electromagnetic Waves – walther – (16180) 2 same for both waves) each wave moves a dis- tance equal to one wavelength, which will be greater for the faster wave. 005 10.0 points From the stands of a race track why do you notice smoke from the starter’s gun before you hear it ±re? 1. The gun smokes before making sound. 2. The response time of eyes is shorter than that of ears. 3. Smoke spreads out quickly. 4. Sound has a much longer wavelength than light. 5. Light travels about a million times faster than sound in air. correct Explanation: Light travels about a million times faster than sound in air, so you see a distant event a million times sooner than you hear it. 006
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## This note was uploaded on 06/07/2010 for the course PHYSICS 58930 taught by Professor Kleinman during the Fall '09 term at University of Texas.

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panda 1 - pokharel(pp7242 Electromagnetic Waves...

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