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)

$3.47\times {10}^{4}C$

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 $13$s protons and $13$ electrons. Magnitude of positive and negative charges is one paise coin

$=NZe=1.67\times {10}^{22}\times 13\times 1.6\times {10}^{-19}C=3.47\times {10}^{4}C$