There are 8.4×1022 free electrons per cm3 in copper, the current in the wire is 0.21A (e=1.6×10−19C). Then the drifts velocity of electrons in a copper wire of 1mm2 cross section will be:-
A
2.12×10−5m/s
B
0.78×10−5m/s
C
1.56×10−5m/s
D
none of these
Medium
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Solution
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Correct option is C)
Number of free electrons n=8.4×1022×106 per m3=8.4×1028 per m3
Current in the wire I=0.21 A
Cross-section of the wire A=1mm2=10−6m2
Thus drift velocity of electrons v=neAI=(8.4×1028)×(1.6×10−19)×(10−6)0.21=1.56×10−5m/s
