✔ 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
