The Science of Electricity Lesson Plan PSTS C

The Science of Electricity Lesson Plan PSTS: C 6 -1 1

Anticipated Problems 1. What are the elements and atoms, and what is the role of electrons in electrical conductivity? 2. What is electricity, and what are the differences between static and current electricity? 3. What is the difference between direct current (DC) and alternating current (AC) electricity? 2

Anticipated Problems 4. What is the difference between the conventional theory of electricity and the electron theory of electricity? 5. What are conductors, insulators, and semiconductors? 6. What are careers related to agricultural electrical systems? 3

Terms alternating current (AC) electrical current atoms electron theory circuit conductors conventional theory current cycle 4 direct current (DC) electricity electrons electrostatic field elements free electron hertz

Terms insulators neutrons polarity protons semiconductors static valence ring 5

Elements are substances that cannot be broken down into simpler substances using ordinary chemical methods. Ø All matter is composed of one or more elements. 6

Atoms are the smallest units of an element. Ø They cannot be divided further without losing physical and chemical properties. 7

Atoms are composed of protons, neutrons, and electrons. Ø The force of attraction between the electrons and the protons keep the atom together. 8

Protons are positively charged elementary particles. 9

Neutrons are elementary particles with no electrical charge. Ø The neutrons hold the protons together. Ø Protons and neutrons make up the nucleus (center) of each atom. Ø Thus, the nucleus of each atom has a positive electrical charge. 10

Electrons are elementary particles that have a negative electrical charge and orbit the nucleus of an atom in rings or shells. Ø Unlike charges attract each other, so the electrons are held in orbit by the positively charged nucleus. Ø Electrons are in constant motion. 11

Electrostatic Field As these electrons move around the nucleus, they actually change their orbit each time around. Ø When viewed, electrons seem to be contained within an invisible force field called an electrostatic field. 12

Electrostatic Field In comparing protons and electrons, the electrostatic field is of the same strength. Ø The positively charged electrostatic field created by the protons has the exact same strength created by the electrons. Ø These two fields are opposite in polarity. Ø For example, Helium has two protons in the nucleus and two electrons orbiting around. 13

Valence Ring Electrons orbit the nucleus of an atom in rings or shells. The rings follow a pattern. Because of distance, electrons in the outer rings will exhibit a lower force of attraction to the nucleus compared to the electrons in the inner rings. The outer ring of electrons is the valence ring. 14

Valence Ring 15

Free Electron A valence electron that breaks away from its atom when it gains energy from an outside force is a free electron. Ø These electrons may drift from one atom to another. 16

Free Electron 17

Electrical Current As this occurs, the movement of electrons being directed through materials is called electrical current. 18

Conductors & Insulators Conductors (e. g. , copper) are substances that contain free electrons and will allow electrical current to flow easily. Insulators are materials that contain electrons that do not share or move freely. 19

Electricity is the flow of electrons from atom to atom in a conductor. Ø The movement of electrons between the atoms is referred to as electrical current. Ø For free electrons to flow through a conductor, an external force must be applied. Ø Electricity is generated because of the external force. 20

Electricity 21

Static is a condition that occurs when there is an imbalance of positively and negatively charged atoms. Ø The electrons are jumping from atom to atom, thus releasing energy. Ø An example is the shock received between two people who touch after walking on wool carpet in cold weather. 22

Current is something produced by moving electrons, and it is measured in amperes. Ø Must flow through a conductor Ø A measure of the amount of energy (flow of electrons) transferred over a period of time. Ø Current electricity may have different sources. 23

Current Electricity Two kinds of current electricity are direct current (DC) and alternating current (AC). 24

Direct Current (DC) Direct current (DC) is a type of electricity in which electrons flow in one direction. Ø In an electrical circuit, electrons flow from the negative terminal to the positive terminal. 25

Fixed Polarity Direct current (DC) sources must have a fixed polarity—a situation in which one terminal is negative and the other is positive. Ø It is usually generated by battery-base electrical systems and is used in the electrical systems of internal combustion engines or in flashlight batteries. Ø Other sources: thermocouples and thermopiles, solar cells, piezoelectric crystals, batteries, fuel cells 26

Alternating Current Alternating current (AC) is electricity that flows first in one direction, stops, reverses, and flows in the opposite direction. Ø After this occurs, electricity has completed one —the steps necessary in a process. 27 cycle

Hertz In the United States, AC electricity is generated by electrical power plants and completes 60 cycles per second. Ø One cycle per second is referred to as hertz. Ø Typically, U. S. electricity is generated and delivered to homes, factories, and schools at 60 Hz. 28

Theories of Electricity Two different theories help describe electricity: Ø The conventional theory Ø The electron theory 29

Conventional Theory The conventional theory is a proposed explanation that says electricity is the flow of positively charged particles through a conductor. Ø The older theory Ø Developed before scientists discovered the existence of electrons Ø It was assumed that current flow in an electrical circuit was from positive to negative 30

Electron Theory Through scientific discovery, electricity is actually the flow of negatively charge electrons through a conductor. Ø The electrons must have a path to and from their source. Ø The path to and from the source is called a 31 circuit.

Electron Theory The flow of electrons in a circuit is from negative to positive. The electron theory is the accepted model of electrical current flow. Ø Because of tradition, the conventional theory is still widely used. Ø Either theory may be used as long as it is used consistently. 32

Conductors (e. g. , copper) that contain free electrons will allow electrical current to flow easily. Ø Also any material composed of atoms having three or fewer electrons in the valence ring. Ø Within these atoms, the electrons are not held tightly. 33

Conductors If any external force is applied, the free electrons can be dislodged. Ø Nearly all metals are good electrical conductors: copper, aluminum, silver, gold 34

Insulators Materials called insulators contain electrons that do not share or move freely. Therefore, insulators do not allow electricity to flow through them under normal conditions. Ø Good electrical insulators include: rubber, plastic, porcelain, glass 35

Insulators Elements or materials composed of atoms with five or more electrons in the valence ring will be insulators. Ø Used to confine the flow of electricity to desired paths 36

Semiconductors are materials that are neither good conductors nor good insulators. Ø Manufactured from elements having atoms with four electrons in their valence rings Ø For instance, silicon and germanium are widely used in making semiconducting materials. 37

Careers The area of agricultural electrical systems can lead to specializations, may provide supplemental skills for most agricultural-related careers, and can lead to business and career opportunities. Ø Explore career opportunities through agricultural courses and/or FFA activities 38

Careers Professional organizations associated with electrical occupations can provide assistance. Ø Several careers are involved within the agricultural electrical systems. 39

Careers Electricians install and service electrical systems. Line workers install and repair power lines or communication cables. Mechanical engineers design, develop, test, analyze, and solve problems. Electrical or electronics drafters will take an engineer’s design to paper for specific technical drawings. 40

Review 1. What are atoms composed of? 2. What is a free electron? 3. What is one difference between static and current electricity? 4. Which theory of electricity is used today? 5. Give one example of a conductor and an insulator. 41