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971_Physics ProblemsTechnical Physics

# 971_Physics ProblemsTechnical Physics - 312*P34.67...

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312 Electromagnetic Waves *P34.67 (a) m V r = = ρ ρ π 1 2 4 3 3 r m = F H G I K J = F H G G I K J J = 6 4 6 8 7 990 4 0 161 1 3 1 3 ρ π π . . kg kg m m 3 b g e j (b) A r = = = 1 2 4 2 0 161 0 163 2 2 π π . . m m 2 a f (c) I e T = = × = σ 4 8 4 0 970 5 67 10 304 470 . . W m K K W m 2 4 2 e j a f (d) P = = = IA 470 0 163 76 8 W m m W 2 2 e j . . (e) I E c = max 2 0 2 µ E cI max = = × × = 2 8 10 3 10 470 595 0 1 2 7 8 1 2 µ π b g e je je j Tm A m s W m N C 2 (f) E cB max max = B max . = × = 595 3 10 1 98 8 N C m s T µ (g) The sleeping cats are uncharged and nonmagnetic. They carry no macroscopic current. They are a source of infrared radiation. They glow not by visible-light emission but by infrared emission. (h) Each kitten has radius r k = × F H G I K J = 6 0 8 990 4 0 072 8 1 3 . . a f π m and radiating area 2 0 072 8 0 033 3 2 π . . m m 2 b g = . Eliza has area 2 6 5 5 990 4 0 120 2 3 π π . . a f × F H G I K J = m 2 . The total glowing area is 0 120 4 0 033 3 0 254 . . . m m m 2 2 2 + = e j and has power output P = = = IA 470 0 254 119 W m m W 2 2 e j . . P34.68 (a) At steady state, P P in out = and the power radiated out is
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