Question

A copper penny has a mass of 3.1gram being electrically neutral, it equal amount of negative positive electrically. What is the magnitude of these charge. A copper atom has positive nuclear charge of 4.6*10^-18 C and a negative charge as equal magnitude.

Answer 1

The number of atoms in copper penny
$$\begin{gathered} n\text{'}=\frac{Avogadrono.}{atomicmassofcu}\times 3.1 \\ n\text{'}=\frac{6.02\times {10}^{23}}{63.5}\times 3.1 \end{gathered}$$
As each atom contains 29 protons and 29 electrons
Total positive or negative charge of the penny
$$\begin{gathered} q=\pm ne=\pm n\text{'}\times 29e \\ =\pm \frac{6.02\times {10}^{23}\times 3.1}{63.5}\times 29\times 1.6\times {10}^{-19}C \\ =\pm 1.37\times {10}^{5}C \end{gathered}$$