A paisa coin is made up of Al-Mg alloy 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.
Treating the paisa coins 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

Mass of coin W = 0.79 g
Molar mass of Al = 26.9815 g
Avogadro number `N_(A) = 6.023 xx 10^(23)`
No. of atoms in 26.9815 g = `6.023 xx 10^(23)`
No. of atoms in 0.75 g = N = ?
`N=(6.023 xx 10^(23) xx 0.75)/(26.9815)`
`=0.16742 xx 10^(23)`
`=1.6742 xx 10^(22)`
Atomic no. of Al, Z = 13. Hence, there are 13 protons and 13 electrons.
`therefore` Amount of positive and negative charge in one coin,
Q = NZe
`=1.6742 xx 10^(23) xx 13 xx 1.6 xx 10^(-19)`
`=3.48 xx 10^(4)` C
`therefore Q = +- 3.48 xx 10^(4)` C
This amount is very large hence, we can conclude that there are positive and negative charges in large amount in neutral matter.