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.

Cells and Batteries Key Points

4.6 Cells and Batteries Key Points

1. An electric cell consists of two electrodes and an electrolyte.
2. Primary cells cannot be recharged, while secondary cells are rechargeable.
3. The zinc-acid cell is not commercially produced because it suffers from polarization and local action.
4. Polarization in cells is the process during which gas bubbles form on an electrode thereby insulating it from the chemical reactions of the cell.
5. Local action is the formation of local cells on the zinc electrode due to iron or lead impurities.
6. The Leclanché cell is the most commonly used wet or dry cell. It consists of a zinc cathode, a carbon anode, sal ammoniac electrolyte and a depolarizer.
7. The dry cell is manufactured in four sizes: D, C, AA and AAA.
8. The mercury cell is constructed small in size for powering small gadgets. It has a very high energy output for its size but due to its high mercury content it has been superseded by silver oxide, zinc air and lithium air cells.
9. Lithium air at the current has the highest shelf life and power output among the so called button or coin cells.
10. The e.m.f. of a cell depends on the materials of its electrodes and electrolyte.
11. Batteries consist of two or more cells connected together to supply large amounts of electric energy.
12. Cells are connected in series to achieve a higher effective voltage source.
13. Cells are connected in parallel to increase the effective current supply.

Atomic Structure Definition Key Points

3.4 Atomic Structure Definition Key Points

1.       Matter is anything that occupies space and has mass.

2.       The smallest particle of matter that can take part in a chemical reaction is called an atom.

3.       An atom consists of protons, neutrons and electrons.

4.       The protons and neutrons form the nucleus of the atom.

5.       Protons and neutrons are collectively known as nucleons.

6.       The atomic number of an element indicates the number of protons in the nucleus of its atom.

7.       The number of electrons in the outermost orbit is the valence electrons.

8.       Electrons carry a negative charge; while protons carry a positive charge. Charged atoms or molecule are called ions.

9.       Most metals contain free electrons which, at room temperatures, roam the spaces between the atoms.

10.    In most substances, atoms team up to form molecules.

11.    Electrons moving in a given direction give rise to an electric current. An electric circuit is a closed path through which an electric current may flow.

12.    Electrically, materials can be grouped as:

a.        conductors,

b.       semi-conductors, and

c.        insulators.

13.    Conductors are those materials which have free electrons. The most common conductors are made of copper and aluminium.

14.    Semi-conductors have few free electrons at low temperatures, but have many free electrons at higher temperatures.

15.    The most commonly used semi-conductors are silicon and germanium. They are used for making diodes, transistors and integrated circuits.

16.    Insulators have no free electrons and do not conduct an electric current.

Occupational Information Network Key Points

2.3 Occupational Information Network Key Points

1.       The four major groups of occupations in the field of electrical engineering are:

a.       Power engineering

b.      Electrical installations engineering

c.       Communications electronics engineering

d.      Industrial electronics engineering.

2.       Across the network of technical occupations, the following personnel cadre are employed:

a.       Artisan

b.      Craftsman

c.       Technician

d.      Engineer.

3.       An artisan is an accomplished operator with a comprehensive knowledge of techniques and the tools used in his or her area of specialty.

4.       A craftsman is a skilled individual talented to perform a range of tasks in his specialty to the required standards.

5.       A technician is a highly skilled worker with both theoretical and practical backing. A technician is directly answerable to the engineer or a technologist.

6.       An engineer is the topmost head of technical teams in large organizations and he is in charge solving design related problems with his respect to his field of specialization.

Safety Key Points

1.10 Safety Key Points

1.       In order to enjoy work and play we must think of our safety and that of others.
2.       Avoid fooling and horse play. There is no fun when you or someone else is hurt.
3.       Dress for safety.
4.       Keep work places and passages clean and clear of unnecessary tools, equipment and materials.
5.       Stores tools, equipment and materials in their properly designed places for safety.
6.       Stores should be well ventilated and lit.
7.       Be familiar with first-aid procedures. Your skills may save the life of a friend.
8.       Be familiar with the position and operation of firefighting equipment.
9. Remember fire extinguisher fighting acronym P.A.S.S. for effective application. It stands for: Pull, Aim, Squeeze, Sweep; meaning:
a. Pull the safety pin from the handle. The pin is positioned at the top of the fire extinguisher. When detached, it releases the locking mechanism and allows discharge the extinguisher.
b. Aim the fire extinguisher nozzle at the base of the fire.
c. Squeeze the lever gently to discharge the reagent.
d. Sweep side to side roughly 15cm or half a foot over the fire until depleted.

10.       Make sure the electric circuits are safe before energizing them.
11.       Never panic in an emergency: This is when you need your reasoning most.