Solutions3_2010

Solutions3_2010 - 1 A copper wire 2 mm in diameter carries...

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the wire and the drift velocity of the electrons. Assume that each copper atom contributes one free electron. Hint: you may need some additional parameters of copper. The additional parameters one needs to solve this problem are molar mass and density of copper. The former is 63.55 g/mol and the latter is 8940 kg/m 3 We use  d I nqAv = where  n  is the number of charge carriers per unit volume, and is  identical to the number of atoms per unit volume since we assume a contribution of 1 free  electron per atom as mentioned above. For copper, which has a molar mass of 63.55, we  know that Avogadro’s number of atoms,  A N , has a mass of 63.55g. Thus, the mass per  atom is atom kg atom g atoms g / 06 . 1 / 06 . 1 10 6 55 . 63 25 22 23 - - = = Thus, n=N/V=N/(m tot / ρ29=Ν/(Ν m atom / ρ29=ρ/ m atom =8940kg /m 3 / 1.06x 10 -25 kg =8.4x10 28 electrons/m 3 Therefore, s m m C m A nqA I v d / 10 5 . 9 ) 002 . 0 )( 4 / ( 10 6 . 1 10 4 . 8 4 5 2 19 3 28 - - - - = - = = π A=C/s Minus sign means that drift velocity of the electrons and the direction of the current are have opposite  directions. 24 points max. 2.   During operation, the effective resistances of a toaster, a microwave oven and an electric frying pan are 20 Ohm, 25 Ohm and 15 Ohm, respectively. If the three are all plugged into a 115 V electrical outlet, what is the total current? What is the total power delivered to these three appliances? I

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Solutions3_2010 - 1 A copper wire 2 mm in diameter carries...

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