Question

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

• 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 $= 0.75\,g$,
Atomic mass of aluminium $= 26.98\,g$
Number of Al atoms in the coin,
$N=\frac{6.02\times10^{23}}{26.98}\times0.75=1.67\times10^{22}$
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
$= NZe = 1.67 \times 10^{22} \times 13 \times 1.6 \times 10^{-19}\, C = 3.47 \times 10^4\, C$