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Physics for Secondary Schools
are all called primary cells. In from coming into contact thereby avoiding the
this type of cell, the current is production of a short circuit. The positive plates
produced from non-recoverable are made of lead dioxide while the negative plates
or irreversible chemical are made of porous lead metal. The two sets of
reactions. For example, when plates with the separators between them are placed
all zinc has been dissolved in in a container filled with a dilute solution of
FOR ONLINE READING ONLY
a simple cell, it will never be sulphuric acid. The term lead-acid refers to the lead
recovered to its original form plates and the sulphuric acid which are the main
by passing a current through the components of the battery. Figure 2.59 illustrates
cell in the opposite direction. the components of the lead-acid accumulator.
Secondary cells Positive terminal
Unlike primary cells, secondary vent caps Negative
terminal
cells can be recharged after Cell
they have run down. Examples connectors Electrolytic
of secondary cells are the lead- Positieve solution
(dilute
acid cell and the nickel-ferrous electrode sulphiric
cell. Secondary cells are also (lead dioxide) acid)
called accumulators. Negative
electrode Protective
casing
Mode of action of lead-acid (lead) Cell divider
accumulator Figure 2.59: Lead-acid accumulator
The lead-acid battery consists
of several lead-acid cells. Charging and discharging the lead-acid battery
Each cell has two groups of When the battery is providing energy, it is said to
lead plates. One group forms be discharging. The energy is produced when the
a positive terminal while the acid (electrolyte) gradually combines with the
other group forms a negative active material of the electrodes. This lowers the
terminal. All positive terminal concentration of sulphuric acid.
plates are connected with a
connecting strap. This is also Charging the lead-acid battery is to drive all the
the case for negative terminal acid out of the plates and return it to the electrolyte.
plates. The positive and During charging (Figure 2.60(b)), a direct current is
negative terminal plates are passed through the battery in the opposite direction
connected so that they alternate. to that during the discharge (Figure 2.60(a)). The
Between the plates are sheets negative terminal of the battery charger is connected
of insulating material called to the negative terminal of the battery, while the
separators. These are made up positive terminal of the charger is connected to the
of porous wood or fibreglass. positive terminal of the battery. This reverses the
The separators prevent the action of discharge and restores the battery to its
positive and negative plates
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Student’s Book Form One
Physics Form 2 Final.indd 84 25/10/2025 10:26
