Question

A coin is made up of Al and weighs $0.75g$. It has a square shape and its diagonal measures $17mm$. It is electrically neutral and contains equal amounts of positive and negative charges. The magnitude of these charges is ( Atomic mass of Al $=26.98g$)

• A. $3.47\times 10^{4}C$
• B. $3.47\times 10^{2}C$
• C. $1.67\times 10^{20}C$
• D. $1.67\times 10^{22}C$

Answer 1

Answer: (A)

Mass of the coin $=0.75g$,
Atomic mass of aluminium $=26.98g$
Number of Al atoms in the coin,
$N=\frac{6.02\times 10^{23}}{26.98}\times 0.75=1.67\times 10^{22}$
As charge number $(z)$ $Al$ is $13$, each atom of Al contain $13$ protons and $13$ electrons. Magnitude of positive and negative charges is one paisa coin
$=NZe=1.67\times 10^{22}\times 13\times 1.6\times 10^{-19}C=3.47\times 10^{4}C$