drift velocity of electrons

2011-05-21 7:23 am

Copper has ρ=9x10^3 km/m^3and 6x10^25 atoms of63.5kg. Assume each copper atom has one free electron. Howlong will a charge take to travel 1m when a current of 2A flows?(Area have10^-6 m^2)

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Copper has ρ=9x(10^3) km/m^3and 6x(10^26) atoms of63.5kg. Assume each copper atom has one free electron. Howlong will a charge take to travel 1m when a current of 2A flows?(Area have(10^-6) m^2)

回答 (1)

天同

2011-05-21 8:11 am

✔ 最佳答案

Density of copper = 9 x 10^3 kg/m3
since molar mass of copper is 63.5 g = 63.5 x 10^-3 kg, and 1 mole of copper consists of 6 x 10^23 atoms (Avogardro's number)
hence, number of copper atoms in 1 m^3 of copper
= (6x10^23/63.5x10^-3) x 9x10^3 = 8.5 x 10^28

Use formula: I = nevA
where I is the current
n is the no. of electrons per unit volume (number density)
e is the eelctronic charge (= 1.6 x 10^-19 C)
A is the cross-sectional area

Thus, 2 = (8.5x10^28) x (1.6x10^-19) v (10^-6)
i.e. v = 1.47 x 10^-4 m/s

Hence, time taken to travel 1 m = 1/1.47x10^-4 s = 6800 s

2011-05-21 00:12:31 補充：
The symbol v represents the "mean drift velocity" of electrons

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