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31_Ch 21 College Physics ProblemCH21 Alternating Current Circuits and Electromagnetic Waves

# 31_Ch 21 College Physics ProblemCH21 Alternating Current Circuits and Electromagnetic Waves

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Alternating Current Circuits and Electromagnetic Waves 231 21.67 Consider a cylindrical volume with and cross-sectional area 3 3 1.00 Liter 1.00 10 m V = = × 1.00 2 m A = The length of this one liter cylinder is 3 3 2 1.00 10 m 1.00 1.00 m V d 3 10 m A × = = = × Imagine this cylinder placed at the top of Earth’s atmosphere, with its length perpendicular to the incident wave fronts. Then, all the energy in the one liter volume of sunlight will strike the atmosphere in the time required for sunlight to travel the length of the cylinder. This time is 3 8 1.00 10 m 3.33 3.00 10 m s d t c × ∆ = = = × 1.00 ( 12 10 × 2 m s The energy passing through the area of the end of the cylinder in this time is ) ( )( )( ) av 1 340 W m 1. 1 E t Intens = ⋅∆ = P 2 2 00 m 3.33 ity A t ⋅∆ = × 12 s 4.47 10 J = 9 × 0 21.68 The capacitance of a parallel-plate capacitor is 0 A C d = e , and its reactance in an AC circuit is 1 2 C X fC π = . Observe that reducing the plate separation to one-half of its
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