A) 10
B) 20
C) 30
D) 40
Correct Answer: C
Solution :
The horizontal force on dust particle\[=qE\]. If v is speed of particle in air, then Viscous force\[=6\pi \eta rv\](Stoke's law) For uniform speed v, we have \[qE=6\pi \eta rv\] If n is the number of excess electrons, then \[q=ne\] \[\therefore \] \[neE=6\pi \eta rv\] Or \[n=\frac{6\pi \eta rv}{eE}\] Substituting given values \[n=\frac{6\times 3.14\times 1.6\times {{10}^{-5}}\times 5\times {{10}^{-7}}\times 0.02}{1.6\times {{10}^{-19}}\times 6.28\times {{10}^{5}}}\]\[=30\]You need to login to perform this action.
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