Download Unit D: Electrical Principles and Technologies

1.4
Cells and Batteries
Figure 1.19 A pacemaker is
inserted just under the skin,
near the shoulder, and
connected to the heart. An
electrochemical cell supplies
the electricity to keep the
person’s heart beating
regularly.
F
D
B
C
A
DRY CELLS
E
A – zinc powder and
electrolyte, where
electrons are released
B – electron collecting rod
C – separating fabric
D – manganese dioxide
and carbon, where
electrons are absorbed
E – negative terminal,
where electrons leave
F – positive terminal,
where electrons return
Figure 1.20 An alkaline dry cell
288
Some people have problems with the small electrical signal that the body
uses to control the beating of the heart. Doctors can implant a device
called a pacemaker to help such people. The pacemaker delivers a small
amount of current at regular intervals to keep the heart beating normally.
The electricity used to operate a pacemaker comes from an
electrochemical cell that supplies a steady current. An electrochemical
cell is a package of chemicals designed to produce small amounts of
electricity. The electricity the cell produces comes from chemical
reactions. The tiny cells used in pacemakers are made with lithium and
iodine and last from 5 to 12 years. Other cells, made with different
chemicals, are used in devices ranging from toys to cars to computers.
There are two main types of cells: dry cells and wet cells.
The electricity-producing cells that we use every day in flashlights and
portable radios are dry cells. They are called “dry” because the chemicals
are in a paste. They are also sealed so they can be used in any position
without the chemicals leaking out. Figure 1.20 shows an example of a
typical alkaline dry cell, used in flashlights and other devices.
The chemical reaction in the cell releases free electrons. These
electrons travel from the negative terminal of the cell, through the
electricity-using device, and back to the positive terminal of the cell.
While at first glance this cell may look complex, it is simply two different
metals in an electrolyte. An electrolyte is a paste or liquid that conducts
electricity because it contains chemicals that form ions. An ion is an atom
or a group of atoms that has become electrically charged through the loss
or gain of electrons from one atom to another. You can learn more about
ions in Unit B: Matter and Chemical Change.
Unit D: Electrical Principles and Technologies