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HW3%20solutions - Weihua Zheng Hw3 Physics 204 Summer 2008...

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Hw3 Physics 204, Summer 2008 Weihua Zheng Part 1 2. (Chp 9 GR 15) Resistance in wire can be calculated by A L R ρ = , we can change the form so that m m m m m mm RA L 85 . 1 10 7 . 1 10 14 . 3 10 7 . 1 ] ) 10 ( 14 . 3 [ 1 10 7 . 1 ] ) 1 . 0 ( 14 . 3 [ 1 8 8 8 2 4 8 2 = × × = Ω × Ω = Ω × Ω = = ρ Watch closely to the transformation of units.(The unit cm Ω in the book is a typo, should be ) m Ω 3. (Chp 9 Problem 7) Two equations solve for two unknown variable L (length) and A (area of cross section). m d d m L m A m L m L m L cm L cm A L A L 4 2 2 8 3 6 3 6 2 8 3 3 10 29 . 2 ) 2 / ( 14 . 3 10 1 . 4 / 10 25 . 24 10 10 7 . 1 10 / 1 10 1 10 × = × = × = = = Ω × = Ω = Ω = = Ω ρ ρ 4,5 omitted. 6.(Chp 9 Problem 5) (a) Ω = + = Ω = + = 15 ) ( 10 ) ( , 5 10 1 10 1 1 ) ( BC R AC R BC R eq eq eq (b) ,at point B current splits, A V I A 2 15 / 30 = Ω = A I I 1 2 1 = = (c) , V I V A BA 20 10 = Ω = V V V V CB 10 20 30 = = , V V CA 30 = = ε (d) , , w R I P A 40 1 2 1 = = w R I P P 10 2 2 1 3 2 = = = w P P P P battery 60 3 2 1 = + + = or use w I P A battery 60 = = ε Part 2.
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