Question

$\frac{4}{25}$ Coulomb of charge contains .................. electrons:

• A. ${10}^{15}$
• B. ${10}^{18}$
• C. ${10}^{20}$
• D. None of these

Answer 1

The correct option is B ${10}^{18}$

Answer is B

The formula for quantisation of charge is given as q=ne.
where, q is the amount of charge in Coulumbs, n is the number of charges and e is the charge on the electron.
In this case, q=4/25 C
So, e = $1.6\times {10}^{-19}C$.
n can be calculated as n=q/e = $\frac{4}{25}\times \left[\frac{1}{1.6\times {10}^{-19}C}\right]={10}^{18}$ which is the number of electrons.
Hence, 4/25 Coulomb of charge contains ${10}^{18}$ electrons:.