Marine electrical-theory

Electrical-Theory – Lesson 1

This is the first lesson Unit in Module 101 in the Electrical Certificate course. It is intended to limit theory and maintain a more practical focus. There are several basic and fundamental theories to understand and these will be covered without delving to deep into complex theories and mathematical formulae. Much of what is covered in the basic electrical theory will be required to understand other modules. In addition understanding basic electrical theory will allow course participants to carry out virtually all of the installation, testing and troubleshooting on most marine electrical and electronic installations.

Electricity – A Basic History

Electricity has a history dating back over 2500 years, when the Greeks discovered the effects created by rubbing amber with other materials. The amber become statically charged and attracted various materials such as feathers, cloth and dry leaves. The Greeks called amber “electron” and the term electric was derived from this original word. It means “to be like amber” or have the power to attract other objects or materials. It took another 2000 years until this phenomena were further explored with various experiments and research. William Gilbert discovered in the early 1600’s that amber was not the only material that could be charged or retain a charge. Gilbert called materials that can be charged “electriks” and those that could not be charged “noelectriks”. In 1773, the Frenchman, Charles DuFay discovered that charged glass could also repel some charged objects and attract others and that the force of repulsion was as important as the force of attraction.

These experiments resulted in the formation of 2 lists.

1. List A included glass rubbed on silk; Glass rubbed on wool or cotton; Mica rubbed on cloth; Asbestos rubbed on cloth or paper and a stick of sealing wax rubbed on wool.

2. List B included Hard Rubber rubbed on wool; a block of Sulfur rubbed on wool or fur; most types of rubber rubbed on cloth; sealing wax rubbed on silk, wool or fur glass or mica rubbed on dry wool, and amber rubbed on cloth.

The materials in List A attract any material in List B. All the materials in List A will repel each other. All of the materials in List B will repel each other. It was Benjamin Franklin named the materials in List A positive and the materials in List B negative. The first material in each list was used as a standard for determining whether the charged object is either positive or negative. Any object repelled by a piece of glass rubbed on silk has a positive charge and any item repelled by a hard rubber rod rubbed on wool will have a negative charge.

Basic Atomic Theory

The atom is the basic building block of everything within the universe and all matter comprises a combination of atoms. Matter is defined as any substance that has mass and occupies space. Matter exists as a solid, liquid, or a gas. An element is a substance that cannot be chemically divided into a simpler substance. An atom is the smallest part of an element. The three principal parts of an atom are the electron; the neutron, and the proton. It is theorized that protons and neutrons are actually made of the smaller particles called quarks

The proton has a positive charge, the electron has a negative charge, and the neutron has no charge. The Neutron and proton combine to form the nucleus of the atom. Since the neutron has no charge, the nucleus will have a net positive charge. The number of protons in the nucleus determines what kind of element an atom is. Oxygen, for example, contains 8 protons in its nucleus, and gold contain 79. The atomic number of an element is the same as the number of protons in the nucleus. The lines of force produced by the positive charge of the proton extend outward in all directions. The nucleus may or may not contain as many neutrons as protons. For example, an atom of helium contains two protons and two neutrons in its nucleus, while an atom of copper contains 29 protons and 35 neutrons.

The electron orbits around the outside of the nucleus. An electron is about three times as large as a proton. The estimated size of a proton is 0.07 trillionth of an inch in diameter, and the estimated size of a proton is 0.22 trillionth of an inch in diameter. Although the electron is larger in size, the proton weighs about 1840 times more.

The Law of Charges

The Law of Charges states that opposite charges attract and like charges repel. This means that two objects with an opposite charge will be attracted to each other. The two positively charged objects and two negatively charged units will repel each other. This is because lines of force can never cross each other. The outward-going lines of force of a positively charged object combine with the inward-going lines of force of a negatively charged object. This produces an attraction between the two objects. If the two objects with like charges come close to each other, the lines of force will repel. As the nucleus has a net positive charge, and electron a negative charge, the electron is attracted to the nucleus.

What are Valence Electrons?

The outer shell of an atom is called the valence shell. Any electrons located in this outer shell of an atom are known as valence electrons. The valence shell of an atom cannot hold more than eight electrons. It is the valence electrons that are important in the understanding of how electricity works. A conductor is made from a material that contains one or two valence electrons. Atoms with one or two valence electrons are unstable and can be made to give up or lose these electrons with minimal effort. Conductors are materials that permit electrons to flow through them easily. When an atom has only one or two valence electrons, these electrons are loosely held by the atom and are easily given up for the current flow. Silver, copper, gold, and aluminum all contain one valence electron and are excellent conductors of electricity. Silver is the best natural conductor of electricity, followed by copper, gold, and aluminum

What is Electron Flow?

Electrical current is the flow of electrons. It is produced when an electron from one atom knocks electrons of another atom out of orbit. When an atom contains only one valence electron, that electron is easily given up when struck by another electron. The striking electron gives its energy to the electron being struck. The striking electron settles into orbit around the atom, and the electron that was struck moves off to strike another electron. Some energy is also lost when one electron strikes another. That is what causes the heat in a wire when current flows through it. If too much current flows through a wire, overheating will damage the wire. If an atom containing two valence electrons is struck by a moving electron, the energy of the striking electron will be divided between the two valence electrons. If the valence electrons are knocked out of orbit, they will contain only half the energy of the striking electron. Material containing seven or eight valence electrons are known as insulators. Insulators are materials that resist the flow of electricity. When the valence shell of an atom is full, the electrons are held tightly and are not given up easily. Examples of insulator materials are rubber, plastic, glass, and wood. The energy of the moving electron is divided so many times that it has little effect on the atom. Any atom that has seven or eight valence electrons is extremely stable and does not easily give up an electron. Electrons can be freed from their orbit by applying an external force, such as movement through a magnetic field, heat, friction, or a chemical reaction.

There are six methods for producing a voltage or electromotive force

1. Friction. Voltage is produced by rubbing certain materials together.

2. Pressure (piezoelectricity). Voltage is produced by squeezing crystals of certain substances.

3. Heat (thermoelectricity). Voltage is produced by heating the joint (junction) where two unlike metals are joined.

4. Light (photoelectricity). Voltage is produced by light striking photosensitive (light sensitive) substances.

5. Chemical action. Voltage is produced by chemical reaction in a battery cell.

6. Magnetism. Voltage is produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through the conductor so that the magnetic lines of force of the field are cut.