ELECTRICITY
In 1767, Joseph Priestly established that electri-cal charges attract with a force inversely propor-tional to distance. In 1800, Alessandro Volta invented the first battery. Michael Faraday (1791–1867) opened the doors of the science we now know as electromagnetism when he pub-lished his law of induction, which simply states that a magnetic field induces an electromotive force in a moving conductor. Thomas Edison (1847–1931) invented the incandescent lamp in 1879, but perhaps even more importantly, built the first central power station and electrical distri-bution system in New York City in 1881. This provided a means of introducing electrical power into industry and the home.
The discovery of the electron by J.J. Thomson (1856–1940) in 1897 introduced the science of electronics and quickly resulted in the inven-tion of the diode (1904), the triode (1907), and the transistor (1946). Andre Marie Ampere established the importance of the relationship between electricity and magnetism. In 1800, Alessandro Volta discovered that if two dissim-ilar metals were brought in contact with a salt solution, a current would be produced, this invention is now known as the battery.
The German physicist George Simon Ohm (1787–1854) proved the mathematical relation-ship between electrical potential (voltage), electrical current flow (measured in amperes) and the resistance to the current flow (mea-sured in ohms: symbol Ω).
Another person who influenced electrical technology was a Scottish inventor named James Watt (1736–1819). James Watt worked in coal mines and saw the power of a horse as it
was used to lift coal from deep in the earth. He developed the steam engine to take over the task of lifting heavy loads instead of using the power of a horse. At the same time, he calculated the work that a horse could do and determined that a horse could walk 165 feet in one minute pulling a 200-pound weight (165 ft. 200 lb. 33,000 ft.-lb. per minute, or 550 foot-pounds of work per second) and called this amount of work one horsepower. One horsepower is needed to lift 550 pounds 1 foot off the ground in 1 second, one horsepower equals 33,000 foot-pounds of work per minute. The term brake horsepower comes from the method of testing the early engines.
In the metric system, the power of engines is measured in watts or kilowatts after James Watt.
Watt’s Law states that a watt is the power done by moving one ampere through a resistance of one ohm using one volt in one second. Horsepower can also be expressed in units of electrical power or watts; the simple conversion is 1 horsepower
= 746 watts.
The term watt is most commonly used to express electrical power, such as the wattage of light bulbs. A light bulb is an example of where watts are commonly used. A 100-watt light bulb requires more electrical power to light than a 60-watt bulb. Electricity is sold in kilo60-watt hours. A kilowatt is 1000 watts and a kilowatt hour is one kilowatt of power being used for one hour.
SUMMARY
The Greeks discovered the first type of electricity in the form of static electricity when they observed that amber rubbed with fur would attract light-weight objects such as feathers. Static electricity is electricity at rest or without any motion. All matter is composed of atoms and electrical charge is a component of all atoms, so all matter is electrical in essence. An atom is the smallest part of an ment that retains all of the properties of that ele-ment. All atoms share the same basic structure. At the center of the atom is the nucleus, containing protons, neutrons, and electrons. When an atom is balanced, the number of protons will match the number of electrons and the atom can be described as being in an electrically neutral state. The phe-nomenon we describe as electricity concerns the behavior of atoms that have become, for whatever reason, unbalanced or ionized. Electricity may be defined as the movement of free electrons from one atom to another.
An electrostatic charge can build up on the sur-face of your body. If you touch something, your charge can be discharged to the other surface, which is called electrostatic discharge (ESD). An automotive technician should always use a sta-tic grounding strap when working with stasta-tic- static-sensitive electronic devices.
When light contacts certain materials, such as selenium and cesium, electron flow is stimulated and is called photoelectricity. Solar energy is light energy (photons) from the sun that is gathered in a photovoltaic solar cell. A photon is pure energy that contains no mass. Thermoelectricity is elec-tricity produced when two dissimilar metals are heated to generate an electrical voltage. A thermo-couple is a small device made of two dissimilar metals that gives off a low voltage when heated.
Piezoelectricity is electricity produced when mate-rials such as quartz or barium titanate are placed under pressure. The production of electricity from chemical energy is demonstrated in the lead-acid battery. Electromagnetic induction is the produc-tion of electricity when a current is carried through a conductor and a magnetic field is produced.
Andre Marie Ampere established the impor-tance of the relationship between electricity and magnetism. Alessandro Volta discovered that if two dissimilar metals were brought in contact with a salt solution, a current would be pro-duced; this invention is now known as the bat-tery. George Simon Ohm showed a relationship between resistance, current, and voltage in an electrical circuit; he developed what is known as Ohm’s Law. James Watt developed a method used to express a unit of electrical power known as Watt’s Law.
Review Questions
1.The general name given every substance in the physical universe is which of the
following:
a. Mass b. Matter c. Compound d. Nucleus
2.The smallest part of an element that retains all of its characteristics is which of the following:
a. Atom b. Proton c. Compound d. Neutron
3.The particles that orbit around the center of an atom are called which of the following:
a. Electrons b. Molecules c. Nucleus d. Protons
4.An atom that loses or gains one electron is called which of the following:
a. Balanced b. An element c. A molecule d. An ion
5.Technician A says the battery provides electricity by releasing free electrons.
Technician B says the battery stores energy in a chemical form. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
6.Static electricity is being discussed.
Technician A says that static electricity is electricity in motion. Technician B says an electrostatic charge can build up on the surface of your body. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
7.What people discovered electricity?
a. The Italians b. The Germans c. The Greeks d. The Irish
8.Technician A says batteries produce direct current from a chemical reaction.
Technician B says that an electrolyte is a chemical solution of water and
hydrochloric acid that will conduct electricity. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
9.Two technicians are discussing thermoelectricity. Technician A says
applying heat to the connection point of two dissimilar metals can create electron flow (electricity). Technician B says a
thermocouple is a small device made of two dissimilar metals that gives off a low voltage when heated. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
10. Technician A says when sunlight contacts certain materials, electron flow is stimulated.
Technician B says solar energy is light energy from the moon that is gathered in a photovoltaic solar cell. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
11. Two technicians are discussing how piezoelectricity works. Technician A says it is electricity produced when barium titanate is placed under pressure. Technician B says when no change in the potential of electrons between positive and negative terminal occurs, the barium titanate creates electricity. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
12. James Watt’s term horsepower is being discussed. Technician A says one
horsepower equals 33,000 foot-pounds of work per hour. Technician B says one horsepower would be produced when a horse walked 165 feet in one minute pulling
a 500-pound weight or 165 ft. ×500 lb. = 33,000 ft-lb. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
13. Technician A says Andre Marie Ampere established the importance of the relationship between electricity and
magnetism. Technician B says Alessandro Volta discovered that if two dissimilar metals were brought in contact with a water
solution, a current would be produced. Who is right?
a. A only b. B only c. Both A and B d. Neither A nor B
LEARNING OBJECTIVES
Upon completion and review of this chapter, you should be able to:
• Explain the terms conductor, insulator, and semiconductor, and differentiate between their functions.
• Identify and explain the basic electrical con-cepts of resistance, voltage, current, voltage drop, and conductance.
• Define the two theories of current flow (conventional and electron) and explain the difference between DC and AC current.
• Explain the cause-and-effect relationship in Ohm’s law between voltage, current, resis-tance, and voltage drop.
• Define electrical power and its Ohm’s law relationship.
• Define capacitance and describe the func-tion of a capacitor in an automotive electri-cal circuit.
KEY TERMS
Ampere Capacitance Capacitor Circuit Conductors
Conventional Theory Current
Ground Insulators Ohm Ohm’s Law Resistance Resistors Semiconductors Voltage
Voltage Drop Watt
INTRODUCTION
This chapter reviews all of the basic electrical principles required to understand electronics and the automotive electrical/electronic systems in the later chapters. An automotive technician must have a thorough grasp of the basis of electricity
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Electrical
Fundamentals
and electronics. Electronics has become the single most important subject area and the days when many technicians could avoid working on an electrical circuit through an entire career are long past. This course of electrical study will cover conductors and insulators, characteristics of elec-tricity, the complete electrical circuit, Ohm’s Law, and finally capacitance and capacitors.