alleryStart learning →A dust particle picks up a net charge of -13 nC. Using the elementary charge e = 1.602 x 10^-19 C, about how many excess electrons does the particle carry?
A8.1 x 10^10 electrons
B8.1 x 10^19 electrons
C2.1 x 10^9 electrons
D1.3 x 10^-8 electrons
Answer & Solution
Correct answer: A. 8.1 x 10^10 electrons
1. Convert the charge to SI units: -13 nC = -13 x 10^-9 C.
2. Divide by the charge of one electron: n = (13 x 10^-9 C) / (1.602 x 10^-19 C) = 8.11 x 10^10.
3. This rounds to about 8.1 x 10^10 electrons.
4. Option B misplaces the exponent by nine powers of ten, and option D never converts the ratio into a whole electron count, leaving units of charge rather than a pure number.
_Source: OpenStax Physics (CC BY 4.0), Ch 18 "Static Electricity", section Transfer and Separation of Charge_
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