A paisa coin is made up Al.Mg alloy and weighs 0.75 g. It has a square shape and its diagonal measures 17mm. It is electrically neutral and constants equal amounts of positive and negative charges . Treating the paisa coin made up of only Al, find the magnitude of equal number of positive and negative charges. What conclusion do you draw from this magnitude ?

Explanation

Atomic number of Al, Z=13
The number of atoms in one mole of a substance `N_A=6.023xx10^23`
Molar mass M=26.9815 g
The mass of coin : m=0.75 g
The number of Al atoms in the coin :
`n=m/M N_A =0.75/26.9815xx6.023xx10^23`
`=1.6733xx10^22` atoms
Each atom of Al has Ze amount of positive as well as negative charge.
`Q=nZe=(1.6733xx10^22)(13)(1.6xx10^(-19)C)`
`=3.48xx10^4` C
We can see that it is a huge amount of charge that is contained in a small coin, which comprises of equal amounts of positive and negative charges.