Aug 16, 2012 Lecturer Name [email protected] Contact Number IT2001PA Engineering Essentials (1/2) Chapter 7 - Cells
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Aug 16, 2012
Lecturer Name [email protected]
Contact Number
IT2001PAEngineering Essentials (1/2)
Chapter 7 - Cells
Chapter 7 - Cells
IT2001PA Engineering Essentials (1/2) 2
Lesson Objectives
Upon completion of this topic, you should be able to:
Describe the constructional features and uses of common batteries.
Chapter 7 - Cells
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Specific Objectives
Define the function of a cell.
State the differences between a primary and a secondary cell.
Describe the construction and operating principles of a simple voltaic cell.
State the factors that effect the electromotive force of a cell.
Identify the following types of cells: Dry Lelanche cells
Mercury cells
Lead-acid cells
Alkaline cells.
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Operating Principles of Cells
Cell
- A device that converts chemical energy to electrical energy.
Battery
- A number of cells connected together.
Types of Cells
- Primary cell
- Secondary cell
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Primary Cell and Secondary Cell
PRIMARY CELL
Can only convert chemical energy into electrical energy.
- CANNOT BE RECHARGED -
SECONDARY CELL
Converts chemical energy into electrical energy and vice versa.
- CAN BE RECHARGED -
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Simple Voltaic Cell
Primary cell
Consists of: a) Copper rod (+ve electrode)
b) Zinc rod (-ve electrode)
c) Dilute sulphuric acid
(electrolyte)
d) Container or casing
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Simple Voltaic Cell
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Operating Principles:
When the zinc and copper rods are connected externally by a wire, a current flows from copper to zinc. Hence, copper is the positive pole (ANODE) and zinc is the negative pole (CATHODE). This current flow is due to the chemical reaction of the cell.
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Polarization
The gathering of Hydrogen bubbles around the copper rod.
This increases the internal resistance and decreases the emf of the cell.
Can be prevented by Depolarizers (eg. Manganese Dioxide)
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Polarization
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Local Action
Due to the impurities (eg. lead, carbon, iron) in the zinc rod.
This reduces the strength of the current.
Can be prevented by coating the zinc rod with mercury.
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Local Action
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Types of Primary CellsTypes of Primary Cells
1.Wet Leclanche Cell
2.Dry Leclanche Cell
3.Mercury Cell
4.Carbon-Zinc Dry Cell
5.Alkaline-Manganese Cell
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Wet Leclanche CellWet Leclanche Cell
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Dry Leclanche CellDry Leclanche Cell
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Mercury CellMercury Cell
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Carbon-Zinc Dry CellCarbon-Zinc Dry Cell
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Alkaline-Manganese CellAlkaline-Manganese Cell
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Types of Secondary CellsTypes of Secondary Cells
1. Lead-Acid Cell
2. Nickel-Cadmium Cell
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Lead-Acid CellLead-Acid Cell
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Nickel-Cadmium CellNickel-Cadmium Cell
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Functions of the Components of a Cell Positive Electrode
Higher potential of the battery terminal.
Negative Electrode
Lower potential of the battery terminal.
Electrolyte
Causes the electrodes to react and produce emf.
Container or Casing
This is the one that holds the electrolyte. The electrodes are not touching the casing.
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Capacity of Secondary Cell
It is expressed in Ampere-hour (Ah).
Capacity of a cell depends on:
a) size of electrodes (plates)
b) number of electrodes
c) amount of acid
d) rate of discharge
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Specific Gravity of Electrolyte
Definition:
This is referring to how acidic the electrolyte is.
A Hydrometer is used to measure the S.G.
Fully-charged battery - S.G. = 1.28
Fully-discharged battery - S.G. = 1.15
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Measuring Specific Gravity of Electrolyte using a Hydrometer
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Next Lesson
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