# How many electrons must be removed from a piece of metal to give it a positive charge of $\;1\times10^{-7} \;C\;?$

$(a)\;6.25\times10^{11}\qquad(b)\;6.25\times10^{19}\qquad(c)\;1.66\times10^{19}\qquad(d)\;3.125\times10^{11}$

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• The SI unit of quantity of electric charge is the coulomb, which is equivalent to about $6.242 \times 10^{18}$ e (e is the charge of a proton). Hence, the charge of an electron is approximately $1.602 \times 10^{?19}$ C.
Answer : (a) $\;6.25\times10^{11}$
Explanation : Let the number of electrons removed be n Then
$n\times1.6\times10^{-19}=1\times10^{-7}$
$n=6.25\times10^{11}\;.$
edited Jan 29, 2014