Page 67 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

• Alkaline cell

• Mercury cell
• Silver oxide cell
• Lithium cell
Types of secondary cell
1 Lead acid cell
2 Alkaline cell or nickel-iron cell

Simple voltaic cell
In 1800, Volta invented the first true battery which came to be known as the voltaic pile. The voltaic pile consisted
of pairs of copper and zinc discs piled on top of each other, separated by a layer of cloth or cardboard soaked in
brine (i.e., the electrolyte).

Construction and working of voltaic cell
It consists of a glass container in which Copper plates and Zinc plates are immersed in dilute sulphuric acid. The
zinc plate act as negative electrode while the copper plate act as positive electrode. When the Copper and Zinc
plates are joined by awire and dipped into dilute sulphuric acid the following observations are made:
The Zinc rod slowly dissolves in the sulphuric acid.Bubbles of Hydrogen are formed on the copper plate.A current
of electrons drifts through the wire from the Zinc to Copper.Dilute sulphuric acid ionises according to the equation.
H SO (aq) 2H (aq) + SO (aq)
2-
+
2
4
4
Zinc atoms dissolves from the Zinc plate and go into solution as Zn ions each of which leaves two electrons
2+
behind on the Zinc rod.
Zn + H SO ZnSO +H
2 4 4 2
These electrons are the source of electron current which goes through the wire from the Zinc to the Copper.
At the Copper rod Hydrogen ions are discharged to form Hydrogen atoms and molecules.
H + e H atom
+
H + H H (g)
2
Current flows from positive terminal of a cell to the negative terminal
Defects of simple voltaic cell

1 Polarisation
2 Local action

54

CITS : Power - Electrician & Wireman - Lesson 13-19