chapter  35
12 Pages

Batteries and alternative sources of energy

The purpose of an electric cell is to convert chemical energy into electrical energy. A simple cell comprises two dissimilar conductors (electrodes) in an electrolyte. Such a cell is shown in Figure 35.1, comprising copper and zinc electrodes. An electric current is found to flow between the electrodes. Other possible electrode pairs exist, including zinclead and zinc-iron. The electrode potential (i.e. the p.d. measured between the electrodes) varies for each pair of metals. By knowing the electromotive force (e.m.f.) of each metal with respect to some standard electrode, the e.m.f. of any pair of metals may be determined. The standard used is the hydrogen electrode. The electrochemical series is a way of listing elements in order of electrical potential, and Table 35.1 lists a

Table 35.1 Part of the electrochemical series

Potassium

Sodium

Aluminium

Zinc

Iron

Lead

Hydrogen

Copper

Silver

Carbon

In a simple cell two faults exist – those due to polarisation and local action.