Question

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?

Answer 1

Step 1: Find number of atoms in one paisa coin.

Given, mass of one paisa coin = 0.75 gm
Molar mass of Aluminum= 27 gm
1 molar mass (i.e., 27 gm) of Aluminum contains $N_A=6.023\times {10}^{23}$ atoms of aluminum.
Number of atoms in one paisa coin
= $\frac{0.75\times 6.023\times {10}^{23}}{27}=1.673\times {10}^{22}$

Step 2: Find magnitude of charge of one paisa coin.

In 1 atom, number of electrons = number of protons = 13

Magnitude of positive charge of one atom = $13\times (1.6\times {10}^{-19})C$

So, magnitude of positive charge of one paisa coin
$q=1.673\times {10}^{22}\times 13\times (1.6\times {10}^{-19})C$
$q=34.8kC$

Final Answer: 34.8 kC