A paisa coin is made up of Al-Mg alloy and weighs 0.75g.
Question:

A paisa coin is made up of Al-Mg alloy and weighs 0.75g. 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?

Solution:

Given, Mass of one paisa coin = 0.75

We know that atomic mass of aluminium = 26.9815

Now, Avogadro’s number = 6.023 × 1023

26.9815 g of aluminium contains 6.023 × 1023 atoms of aluminium

Number of atoms in (0.75 g of aluminium or) one paisa coin = [0.75 × 6.023 × 1023]/26.9815 = 1.6742 × 1022

One Aluminum atom contains 13 protons or 13 electrons and magnitude of charge of one atom =

Now, magnitude of charge one paisa coin = (Number of atoms in one paisa coin) × Charge of one atom) = (1.6742 × 1022) × [13 × (1.6 × 10‒19)] = 34.8 kC.

From this one can easily understand that ordinary atom has large amount of charge.

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