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Unformatted text preview: aldawsari (ma28683) – HW17 – Betancourt – (16856) 1 This printout should have 9 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 32.132.6 001 10.0 points In a particular medium the speed of light is sixsevenths that of the speed of light in vacuum and the electric field amplitude has a maximum value of 7 . 4 mV / m. The speed of light is 2 . 99792 × 10 8 m / s . Calculate the maximum value of the mag netic field. Correct answer: 2 . 87977 × 10 11 T. Explanation: Let : E = 7 . 4 mV / m and c = 2 . 99792 × 10 8 m / s . The index of refraction is n ≡ c v , so the index of refraction of light in this particular medium is sevensixths. According to Maxwell’s laws, for an elec tromagnetic wave, the relation between the amplitude of the electric field and the magni tude of the magnetic field is given by E = c n B = v B , where n is the index of refraction and v is the velocity of light in that medium. For our problem n = 7 6 since v = 6 7 c , so the maximum value of the magnetic field is B = 7 6 E c = 7 6 7 . 4 mV / m 2 . 99792 × 10 8 m / s · V 10 3 mV = 2 . 87977 × 10 11 T . 002 (part 1 of 2) 10.0 points The cable is carrying the current I ( t ). Evaluate the electromagnetic energy flux S at the surface of a long transmission cable of resistivity ρ , length ℓ and radius a , using the expression vector S = 1 μ vector E × vector B . 1. S = μ ǫ ρ I 2 π a 2 2. S = ǫ μ I 2 2 π a 2 3. S = ρ ℓ I 2 π a 2 4. S = μ I 2 2 π a 2 5. S = π a 2 I 2 ρ ℓ 6. S = ρ I 2 2 π 2 a 3 correct 7. S = I 2 4 π μ c ℓ 8. None of these....
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 Spring '10
 Gavrine
 Energy, Light, Correct Answer, Pnet

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