How electricity is generated Reviews Exercises
5.10 How electricity is generated Reviews Exercises
1. Define the term “generator."
2. State the three major parts of a direct current generator.
3. With the aid of a sketch, explain how e.m.f. is induced in a direct current generator.
4. Explain how a simple direct current generator may be improved for greater e.m.f. induction.
5. Define the term ''piezoelectricity."
6. With the aid of sketches, explain how thermocouples may be used to produce a higher voltage.
7. Explain how solar cells produce electricity.
8. List three applications of solar cells in everyday life.
9. State two uses of geothermal energy.
How electricity is generated Key points
5.9 How electricity is generated Key points
1. A D.C. generator produces a unidirectional voltage and current.
2. The three major parts of a D.C. generator are stator, rotor and commutator.
3. The direction of the induced e.m.f. in straight conductor is determined by the Right-Hand Rule.
4. The direction of the induced e.m.f. in coil conductor or solenoid is determined by the Right-Hand Grip Rule.
5. Electrical energy may be generated by ways other than magnetism and chemical action.
6. A piece of electric crystal can generate electricity when subjected to a changing pressure across two of its sides (compressed or released).
7. A steady pressure applied to a piece of electric crystal will not generate electricity.
8. The most frequently used piezoelectric crystals are quartz, Rochelle salt and barium titanate.
9. Electricity is produced whenever there is a relative motion between two materials such as a glass rod and silk. This is called static electricity. We can simply say that electricity is produced by friction.
10. Radiant energy is another source of electricity:
a. a photovoltaic cell converts light energy into electricity,
b. all photovoltaic cells are composed of two layers of dissimilar semi-conductor materials.
11. When a light ray strikes the junction between the two layers of a photovoltaic cell, electrons are forced across it.
12. Modern solar cells are made of silicon and germanium semi-conductor material.
13. Geothermal energy is heat energy produced within the Earth.
14. Geothermal power is renewable and environmentally friendly.
What is geothermal power
5.8 What is geothermal power
Geothermal energy is heat energy produced within the Earth.This form of energy is formed in two ways:
(a) When the earth was originally created (very small fraction of about 20 %)
(b) When radioactive elements disintegrate within the earth crust (about 80 %)
Even though the geothermal may occur deep within the earth crust, heat conduction can take place up to the earth’s surface or should there be liquids like water on the way, these may easily signify the earth’s internal heat existence in terms of geysers (hot springs) or vapours. If the temperatures are high, as much 4000 0C, internal elements may melt and float on their parent solid elements. Water on the other hand, is superheated to high as 370 0C. . The heat energy so produced is used heat water at the heat exchanger. This has kinetic energy that is in turn directed to spin turbine. The turbine converts kinetic energy to electrical energy. A part from electrical energy supply, heat from geothermal can also be regulated for heating in homes.
Geothermal power is renewable and environmentally friendly. The number of users has incredibly increased due to advancement in technology, however it suffers from limitation of its location and dear cost of construction of power plants.
It is believed theoretically, geothermal power if highly exploited, will eventually lower the impact the global warming.
The reliability of geothermal power has enabled this form of energy to be injected into the national grid to boost national power distribution.
Photovoltaics
5.7 Photovoltaics
A photovoltaic or solar cell consists of a rectangular or round piece of metal covered with a thin, transparent layer of oxide as shown in Fig. 5.7.1 The light rays striking the oxide layer penetrates this layer and then the junction between the oxide and the copper. The light rays force the electrons to flow across the junction, and so generating electricity.
When the light rays are interrupted, the e.m.f. generated by them disappears at the same instant. A photovoltaic cell made of copper and copper oxide is very inefficient. Modern solar cells are made of silicon which is a semi-conductor. These are more effective than those made of copper, Fig. 5.7.2.
Photovoltaics are used in a wide variety of modern electrical and electronic devices. A few applications are:
(a) Spacecraft power supplies.
(b) Light meters.
(c) Automatic-operated switches.
(d) Burglar alarms.
(e) Cellphone chargers.
(f) Home lighting.
Although photovoltaics depend on light for their operation, exposure to heat may damage them.
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