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The number density of free electrons in a copper conductor estimatedis 8.5 xx 10^(28) m^(-3). How long does an electron take to drift from one end of a wire 3.0 m long to its other end ? The area of cross-section of the wire is 2.0 xx 10^(-6) m^(2) and it is carrying current of 3.0 A. |
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Answer» Solution :If free electrons drift through length l of a given wire in time t then their drift SPEED is, `v_(d) = (l)/(l)` Now, CURRENT passing through given wire is, `I = Av_(d) ` ne `therefore I = A ((l)/(l)) ` ne `therefore t = ("Alen")/(I)` `therefore t = (2 xx 10^(-6) xx 3 xx 8.5 xx 10^(28) xx 1.6 xx 10^(-19))/(3)` `therefore t = 27200 s ` Note : If above time is asked in h, min and s then : `therefore t = (27200)/(3600) ` h `therefore t = 7.556 `h ` therefore t = 7 h + (0.556 xx 60) ` min ` = 7 h 33.36 ` min 7h 33 min + `(0.36 xx 60)` s `therefore t = 7 h 33 ` min 22 s |
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