Atomic Structure Review



Atomic Structure Review

Low mass particles called electrons orbit a very dense nucleus composed of two types of high mass particles called neutrons and protons. Relative to the size of the particles, the distance between the nucleus and the orbiting electrons is very large. Atoms are mostly empty space.

Electrons have a negative charge and very low mass compared to neutrons and protons.

Electrons are arranged in layers called energy levels at different distances from the nucleus of their atoms. There are limits to how many electrons can be in each energy level.

Protons have a positive charge and very high mass compared to electrons.

Protons are packed closely together with neutrons in the nucleus.

Neutrons have no charge and very high mass compared to electrons.

Neutrons are packed closely together with protons in the nucleus.

Protons and neutrons have nearly the same mass, It would take more than 1,800 electrons to balance the mass of one proton or one neutron.

The protons and neutrons are packed very close together compared to the electrons in the energy levels. Usually, positively charged particles strongly repel each other, but in the nucleus of atoms another force called the “strong force” overpowers the force of repulsion and keeps the protons close together. The strong force is provided by smaller particles known as “gluons”.

The three main particles (protons, neutrons & electrons) are made of smaller particles. Protons and neutrons are made of quarks. Electrons are made of leptons. Many other small particles play important roles in the nucleus. If you wish to know more about these particles and their function, research the term “particle physics” on the Internet or in a modern encyclopedia.

Conductors & Insulators

In atoms of metallic elements, (3 electrons or less in the outer energy level) like the lithium atom shown above, the outer electrons are weakly held compared to atoms of elements that have 4 or more electrons in the outer energy level. Because of this,

the electrons in a solid or liquid piece of metal share their outer electrons rather than keeping them in orbits around particular atoms. The outer electrons move randomly from atom to atom within the piece of metal. This property allows metals to “conduct” an electrical current easily. Therefore, metals are known as good conductors of electricity.

Materials called insulators do not conduct electricity easily because the outer electrons in their atoms are strongly attracted to each individual atom and cannot easily be made part of an electrical current.

Electricity

Electricity is usually thought of as electrons that are moving or have moved from one atom to another. If there is a continuous stream of electrons, they are described as an electrical current. If an excess of electrons have collected on an object, but are not moving they are described as a static electricity.

Static Electricity & Charging

Atoms are electrically “neutral”. This means that the positive charges (protons) are balanced exactly by an equal number of negative charges (electrons).

A neutral object that gains electrons becomes negatively charged.

When a neutral object loses electrons, it becomes positively charged.

If the charged object was originally a single atom, molecule or small group of atoms the charged particle is referred to as an ion.

A large object can acquire a considerable “charge”. Lightning is the result of a large accumulation of charge. Lighting is one of the most dramatic forms of electrical discharge.

Smaller electrical discharges can be observed when static electricity causes a spark to jump from one object to another (like when we pull a sweater off over our head). Electrical discharges are the result of “grounding” an object after charge builds up. If the object is “grounded” continuously, charge will not build up on the object and electrical discharge will be prevented. Lightning rods serve this purpose by draining off charge as it starts to accumulate on buildings and towers. Lightning rods are not designed to conduct lightning discharges to the ground. Lightning carries enough electrical current to vaporize large diameter copper wire.

Current Electricity

Current electricity is subdivided into two types, DC and AC. All current electricity in solids can be described as a flow of electrons.

DC (direct current) flows only in one direction… from a negatively charged place to a positively charged place. In a battery powered circuit the electrons will flow from the negative terminal to the positive terminal when connected with a conductor.

AC (alternating current) reverses direction many times per second. Household electricity is AC. AC has one big advantage over DC. We can raise and lower the voltage using transformers. We will discuss how this is possible and why it is necessary later in this unit.

Electrical Circuits

Electrical circuits are pathways for electrons.

1. Complete Circuits - Complete circuits give electrons an unbroken pathway from the source (battery, etc.) through the conductors and back to the source.

2. Safe Circuits - electrons in the circuit travel through an electrical device that uses their energy safely (light bulb, motor, etc.) and back to the electron source.

3. Short Circuits - electrons travel in a direct pathway from the source directly back to the source without passing through a device that uses the energy safely.

4. Whenever electrons flow in a conductor, part of their energy is converted to heat energy.

5. Short circuits can cause damage to the circuit wiring and other components through overheating and may cause serious burns or fires to occur.

All circuits have two possible conditions.

6. In the closed condition the circuit is a “complete” circuit and is said to be “on”.

7. In the open condition the circuit is “incomplete” or “broken” and is said to be “off”.

Electricity does not flow through an open circuit.

Properly constructed electrical circuits have several common features. They must have

8. a source of power (AC or DC power supply),

9. conductors (pathways for the electrons), and

10. some sort of device designed to use the electrical energy (sometimes called the “load”).

Two other very common features are switches (to open and close the circuit) and fuses or circuit breakers (to protect the circuit from overheating).

All of the components of a circuit must be designed to safely handle the amount of current flow required by the circuit. It is necessary to consider the voltage and amperage (or wattage) ratings of all components before installing them in a circuit. Failure to use components with sufficient rating will result in damage to the circuit and may cause one or more components of the circuit to overheat. Overheated circuits are responsible for many vehicle and building fires.

Two Basic Electrical Circuit Classes

All electrical circuits can be classified as series or parallel circuits (or a combination of the two).

In series circuits, the current passes through devices in sequence (first through one, then through a second, etc.). If any of the devices fail to conduct the current, all current flow stops in the circuit.

In parallel circuits, the current flows through two or more devices simultaneously. If one device fails, the current will still flow through the other device(s).

Safety

11. Do not experiment with household current (110-240vac).

12. All of the components of a circuit must be designed to safely handle the amount of current flow required by the circuit.

13. It is necessary to consider the voltage, amperage and wattage ratings of all components before installing them in a circuit.

14. If a short circuit will cause overheating, a fuse or breaker of the proper rating must be used to prevent damage (Low current circuits like flashlights and watches usually do not require fuses or circuit breakers).

15. Failure to use components with sufficient rating will result in damage to the circuit and may cause one or more components of the circuit to overheat.

16. Overheated circuits are responsible for many vehicle and building fires.

Our Lab Electricity

17. The electricity we use in the electricity labs in this class is direct current electricity (DC). We do not experiment with common household electricity because it is deadly. More people are killed with common household (110-125 volt AC) current than any other form of electricity.

18. Under most circumstances, the DC electricity that we use in our labs will not hurt you. Your body has too much resistance for the current to reach your heart or brain. However, some people have suffered tissue damage while using our lab equipment in an inappropriate manner.

19. Several students have “tested” the voltage by placing the power clips on their tongue. This resulted in some tissue destruction.

20. One student connected the power clips to his braces. The result was the death of one of his teeth.

21. Another student connected the power clips to his earring. The student suffered considerable pain in his left earlobe for several days.

22. The voltage at the source (a wet cell, deep-cycle, RV/Marine battery) is about 13.8 volts.

23. The voltage at your stations is about 11 - 13 volts.

24. Your station is protected by a 3.1 ampere circuit breaker and controlled by a SPST (single-pole single-throw) switch.

25. When the circuit is closed (switch is “on”), the LED (light emitting diode) beside the switch will light up.

26. When you touch the power clips together, a “short circuit” will result which will cause your breaker to “break” or “trip”.

27. The breaker can be “reset” by pushing the reset button.

28. If two or more stations are “short circuited” at the same time, the main 10 amp circuit breaker will trip. If this occurs too often, the lab exercise will be discontinued.

29. A 10 A circuit breaker near the battery protects the entire DC lab circuit complex.

Terminals

A terminal is a place where electrons (or other charged particles) can enter or leave an electrical component (battery, switch, light bulb, electrical outlet, etc.).

Negative Terminals - Electrons flow out of this terminal on batteries and other manmade sources of DC electricity.

Positive Terminal - Electrons flow into this terminal on batteries and other manmade sources of DC electricity.

Appliances (radios, GPS units, LED devices, etc.)

Negative Terminal - This terminal must be connected to the negative terminal of the energy source. Electrons flow into this terminal from the energy source.

Positive Terminal - This terminal must be connected to the positive terminal of the energy source. Electrons flow out this terminal back to the energy source.

Classifications of Electricity

Static electricity is an accumulation of electrons or other charged particles can produce a "static charge" which when discharged becomes current electricity of short duration. This is often referred to as "static discharge".

For example, a wool sweater will lose some of its electrons to a cotton shirt because the atoms in the cotton have a stronger attraction for the electrons in the wool. This results in the sweater having a positive charge and the shirt having a negative charge. When the shirt and sweater are separated, some of the electrons are pulled back to the sweater causing “static discharge”. Before the shirt and sweater are separated, they have an attraction for each other because of the difference in charge. This attraction has come to be known as “static cling”. Some fabric softeners are formulated to provide a very thin coating of insulating chemical on the fibers of clothing. This coating prevents or reduces the transfer of electrons or ions and effectively prevents “static cling”.

Other static electricity events can be seen in rooms with dry air and carpeted floors. A static charge can be collected as we walk along the carpet and discharged later when we touch something that is “grounded” (like an electrical appliance that is plugged into a grounded outlet). Although they are short lived, static discharges that take place in our houses can be thousands of volts (enough to zap your computer or CD player if they are not built properly.).

Another example of static discharge is lightning. Lightning is static discharge between clouds or between clouds and earth. Lightning bolts have millions of volts of force pushing (or pulling) them. Electrons and ions (larger charged particles) can be transferred between clouds or between clouds and the ground resulting in a “charge” being built up in both places. When the difference between the two opposite charges becomes great enough, a massive flow of electrons (lightning) occurs between the two objects.

Current electricity is a flow of electrons... electrons moving from one place to another. The electrons are forced to move by the attraction or repulsion of protons or other electrons. Current electricity is generally classified as DC (direct current) or AC (alternating current).

DC (direct current) is electricity that flows only in one direction. Static discharge electricity is DC. Electricity produced by chemical (voltaic) cells, batteries, and solar cells is also DC.

AC (alternating current) gets its name from the fact that the electrons reverse direction many times per second. The electricity we use in our homes is AC. There are many other sources for AC such as radio waves, light waves, microwaves and radar waves.

SOURCES OF ELECTRICITY DC (direct current) is the most “natural” form of electricity. Every time we experience the spark or shock from the discharge of a static electricity charge we are seeing or feeling direct current electricity. Of course, lightning is our most powerful source of DC. Other sources of DC are chemical cells, photovoltaic cells, fuel cells and batteries made from a combination of cells. AC (alternating current) occurs in nature, but the alternating current we use the most is produced at electrical power plants by the use of “alternators” turned by steam power.

CONDUCTORS, INSULATORS, RESISTORS

CAUTION!! Anything will conduct electricity if the voltage is high enough... even air!

A conductor is a material that allows electrical charges to pass through it easily. The most common conductors are metals. In solid conductors, electrical current is in the form of electrons, but in liquids, gases and plasmas the current is a flow of charged particles called ions.

Metallic conductors are composed of atoms that have a weak attraction for their outer electrons. The outer electrons of metallic atoms are free to roam around from atom to atom in a sort of “electron soup”. When connected in a complete circuit to a voltage source (battery, generator, etc.), the free electrons are forced to flow in an electrical current away from the negative terminal, through the circuit and back to the positive terminal of the voltage source.

Electrolytic solutions like salt water or water with a lot of dissolved minerals are better conductors of electricity than pure water because they contain more ions. Ordinary drinking water does not conduct low voltage electricity very well, but will conduct household electricity well enough to kill you.

Insulators are usually composed of atoms that have a strong attraction for their valence (outer) electrons making it difficult to move them from atom to atom. In some insulators, the electrons are not free to move because they are involved in a strong chemical bond with other atoms.

Resistors are made of materials that reduce the flow of electrons from atom to atom. This “resistance” occurs because of a strong attraction between the nucleus of the atoms in the material and the passing electrons.

VOLTAGE, AMPERAGE, AND RESISTANCE

Voltage refers to the electrical "force" that moves the electrons. It is sometimes referred to as "electrical potential" or "electromotive force" (EMF). The metric unit used to measure voltage is the volt (V).

The speed of electricity through the best of conductors is close to 300,000,000 meters per second (about 186,000 miles per second).

Normal flashlight voltages range between 1.5 VDC and 18 VDC. A car battery usually produces 13 to 15 VDC. In case you haven't figured it out already, VDC means "volts direct current". House electricity usually is moved along with a force of 110-125 VAC (volts alternating current). Some household appliances (water pumps, clothes dryers, stoves, air conditioners, etc.) may need 220-240 VAC, which is also available at your main electrical panel.

You should remember that more people are killed with 110-120 VAC electricity than any other voltage. It is dangerous if not used safely. KEEP YOURSELF OUT OF THE CIRCUIT!!

Amperage refers to the "current" or number of electrons flowing past a point each second. The metric unit used to measure electrical current is the ampere (A) and is equal to 6.24 x 1018 electrons (6,240,000,000,000,000,000) passing a point in a second. In order to make things easier we call this number of electrons a coulomb (C). So, one coulomb per second is equal to one ampere. (1C/s=1A). The term ampere is usually shortened to amp.

Excessive current flow through a conductor or device can cause overheating.

Resistance is a term used to describe how much a material restricts the flow of electricity. Resistance to the flow of electricity comes from the attractive force of the protons in the nuclei of the atoms making up the material. A strong attraction between the protons and passing electrons produces higher resistance to electrical current (the flow of electrons).

The metric unit used to measure electrical resistance is the ohm. The symbol for the ohm is the Greek letter omega (. Resistance causes electricity to be transformed into heat and, in most cases represents an unintentional loss of energy (inefficiency).

Some materials have a very low resistance to electric current and are called CONDUCTORS. Conductors are made of materials in which electrons can easily be made to jump from atom to atom.

Materials with a very high resistance are called INSULATORS.

In order for electrons to "flow" in a material, the outer electrons of the atoms making up the material must be "loose", or weakly attracted by the nuclei of the atoms making up the material.

We have yet to discover a material that is the perfect insulator or conductor. All materials have some resistance and some conductance (the opposite of resistance). If the voltage is high enough, anything will conduct electricity.

Resistors are devices specifically designed to "resist" or restrict the flow of electrons. Resistors are primarily used in electronic devices.

Note: Some resistors are “variable resistors”. That means that the resistance can be changed by a rotary or slide mechanism. Another name for a variable resistor is potentiometer or “pot”. Volume controls, light dimmers & motor speed controls are all variable resistors.

Fuses & Circuit Breakers

Overheated electrical components may result in an electrical fire or other damage to the device. Fuses and circuit breakers are designed to interrupt the flow of current if it becomes excessive. Fuses have a metal strip inside that melts when the circuit is overloaded. Circuit breakers have an automatic thermal or magnetic switch that turns the circuit off when too much current is being used. Fuses are cheaper than circuit breakers, but they are not reusable. Because fuses are easily replaced, people without a good knowledge of electricity can accidentally cause a hazardous situation by replacing a fuse with one that has more current carrying capacity. Using a larger fuse is dangerous because the wiring may not be able to safely conduct the same amount of current as the larger fuse. Since circuit breakers are not easily or cheaply replaced, they are considered to be a safer device for protecting home circuits.

Wire size must always be considered when working with electricity. Larger diameter wire of the same material can conduct more current than smaller wire. Wire size is rated with the “gauge” system. Larger wire will conduct electricity better with less loss of voltage due to resistance. Most house wiring is 12 gauge (12 AWG). Larger wire (10 ga.) is used for clothes dryers and hot water heaters. Even larger wire (8 ga.) is used for electric stoves. Extension cord wire is usually 18 ga. or 16 ga. and cannot safely conduct as much current as house wiring. A short extension cord is preferable over a long one because as the cord length increases so does the energy loss due to resistance. Extension cords with larger wire size are preferable because they will conduct electricity with less loss of energy due to resistance. Never use a fuse or circuit breaker with a higher amperage rating than that of the wire in the circuit.

Electricity From Cells & Batteries (DC)

DC (direct current) is electricity that flows only in one direction. Static discharge electricity is DC. Electricity produced by chemical (voltaic) cells, batteries, and solar cells is also DC.

Some DC devices (radios, TVs, CB radios, CD players, etc.) can be damaged if the current flows the wrong way. To prevent damage from “polarity reversal”, some manufacturers insert a diode in series with one of the power socket wires. Diodes will allow electricity to flow only in one direction. If a device is “diode protected” against polarity reversal, no damage will occur if the positive and negative power leads are reversed. The device simply will not work because the diode prevents any current flow.

Batteries are made up of “cells”. Normally, when we think of cells and batteries we think of the type used in flashlights, portable radios, cars & trucks, garage door openers, etc. These are “electrochemical” cells and batteries. A single electrochemical cell may also be known as a “voltaic” cell (named after Allesandro Volta, the Italian physicist who invented the “voltaic cell” and “voltaic pile”). The term “wet cell” refers to the liquid electrolyte used in the cells of most automotive, marine and aircraft batteries. “Dry cells” contain electrolyte in solid or paste form.

Normal flashlight voltages range between 1.5 VDC and 18 VDC. A car battery usually produces 13 to 15 VDC.

Different voltages in batteries are achieved by connecting different numbers of cells in series with each other. This means the negative terminal of one cell is in contact or connected to the positive terminal of the next cell.

Different current ratings (amperage) and charge holding capacities are achieved by connecting different numbers of cells in parallel with each other. This means the negative terminal of one cell is connected to the negative terminal of the next cell. Likewise, the positive terminals of the cells are all connected to each other.

If both higher voltage and higher current (amperage) ratings are required, a series-parallel battery can be constructed with several series batteries can be connected in parallel with each other (the negative terminals of all the batteries connected together and the positive terminals of all the batteries hooked together). Most automotive batteries are series-parallel construction.

We have all used cells and batteries. The common designations of “D”, “C”, “AA” and “AAA” all apply to the different sizes of cells even though they are improperly labeled as batteries on the package. Miniature flashlights often operate with a single cell. Larger flashlights may use six cells or more. The operating voltage of a flashlight that takes a single “AA” or “AAA” cell is about 1.5 volts. The operating voltage of a 2-cell flashlight is usually about 3V and a six-cell flashlight normally has an operating voltage of 9V.

Photovoltaic cells (also known as solar cells) are devices that, when connected as part of a complete circuit, produce direct current electricity when exposed to light. Up to the limits of the device, an increase in light intensity will increase electrical current available for the circuit. Like the cells we use in flashlights, photovoltaic cells may be connected in series or parallel or series-parallel to produce higher voltages and currents. Like automotive batteries, photovoltaic arrays (batteries) are usually a large number of cells connected in a series-parallel configuration.

Fuel cells, like the common flashlight cell are also electrochemical devices, but they produce electricity by using a fuel that may be replenished. Natural gas (methane) is often used as the fuel in earth-bound applications. The United States Space Shuttle fleet uses fuel cells powered by hydrogen to produce electricity and water.

Electricity From Electrical Power Companies (AC)

AC (alternating current) gets its name from the fact that the electrons reverse direction many times per second. The electricity we use in our homes is AC. There are many other sources for AC such as radio waves, light waves, microwaves and radar waves.

Electric company generators (often called alternators), which get their energy from high-pressure steam or other gases, produce most AC. Steam is produced by boiling water with a coal or oil-burning boiler. The steam is allowed to build up pressure before it is released through nozzles to spin high-speed turbines. Steam driven turbines are connected to the alternators that produce the electricity.

How Electricity Is “Generated”

When a magnetic field and a conductor move across each other, electrons are forced to move along the conductor if it is a part of a complete circuit. One of the two, either the magnetic field or the conductor, must be moving in order to force the electrons into motion.

Whenever electricity starts to flow in a conductor, a magnetic field expands or “grows” outward from the conductor. In wires the magnetic field surrounds the wire for its entire length as long as the current of electrons is flowing. When the electrons stop flowing, the magnetic field collapses back into the wire. Keep in mind that this expanding and collapsing magnetic field is a magnetic field in motion (but only while it is either expanding or collapsing).

How does the magnetic field move electrons? If we imagine a flexible, clear plastic hose full of steel marbles, we can see the action of a magnetic field. If we hook the ends of the tube together to form a continuous loop and if a strong enough magnet is used, the steel marbles can be made to move around the loop without actually touching them. As we move the magnet along the outside of the tube, the magnetic field forces the marbles to move along the loop with the magnet. Alternating current (AC) is generated in much the same way.

Inside generators are giant magnets that spin near large coils of wire. When the magnetic field from the magnets moves through the wires it causes electrons to move in the wires that lead from the coils to the electrical transmission lines outside.

Getting The Electricity To Us

One of the problems in the early days of electrical power generation was resistance. Remember that resistance is the term used to describe forces within the atoms that oppose the flow of electrons through a conductor. Mr. Edison’s first commercial generators produced DC electricity. Those customers close to the generating plant had plenty of voltage, but those who lived at the end of the line had much lower voltage (dimmer lights). Mr. Edison’s solution was to build lots of small power plants. Mr. Westinghouse had a better plan.

Thanks to Mr. Westinghouse and his employees, the electric power companies now use alternating current. They use AC because its voltage can be "stepped up" or "stepped down" by the use of devices known as "transformers". This feature of AC gives us many advantages. The main advantage is that every house in the United States can receive pretty much the same voltage electricity from the power company. Due to voltage drops caused by resistance in the power lines, this convenience was not possible with DC power plants. Of course, this means that “step-up” transformers must be located in many places between the power company generators and our communities in order to counteract the effects of resistance in the lines. Near our homes and businesses are “step-down” transformers to give us the lower voltage required to run our appliances.

Transformers

Transformers are devices containing two or more coils of wire that are very close together, but not physically connected. The coils of wire are wrapped around an iron or iron alloy core to make the transformers more efficient.

The wire making up each coil is coated with a very tough, high voltage insulating material to prevent "short circuits" due to contact between the wires. Each coil has hundreds or even thousands of "turns" or wraps of wire. Electric power company transformers are located outside our homes. They can be seen high on utility poles or mounted in large, insulated boxes on the ground.

Back at the electric power company, their alternator is connected to one of the coils (the primary coil) in the first “step-up” transformer outside the power generation building. When the power company alternators are in operation, the other coils inside the transformer (secondary coils) are subjected to the expanding and contracting magnetic field caused by the alternating current. This expanding and contracting magnetic field causes electrons to flow in the secondary coils of wire even though they are not physically connected to the primary coil.

Here is the advantage of AC. If the unconnected coil (the secondary coil) has a different number of "turns" than the primary coil, the voltage will be different than it is in the primary coil.

More turns on the primary than on the secondary will cause the voltage to be lowered. More turns on the secondary than on the primary will cause the voltage to be raised.

The transformer on the pole near your house is a "step down" transformer because it lowers the voltage from thousands of volts to about 240 volts.

Other examples of "step down" transformers are the “power cubes” or “power supplies” that allow us to operate portable CD players, radios, etc., on household electricity. Inside the black plastic boxes are coils of wire that make up a “step down” transformer and a diode circuit that converts the AC to DC.

Note: These devices are using electricity any time they are plugged into the wall outlet even if the CD player or other device is not turned on. When the transformer is plugged in electricity constantly flows through the coils of wire inside the box. The resistance of the wire causes the electricity to be converted to heat energy even nothing is being powered by the unit.

Most televisions and microwave ovens have a “step up” transformer in the back that boosts the voltage from 120 V to 30,000 V or higher. Do not disassemble these appliances or poke things inside the ventilation holes! The electricity stored in the television and microwave oven circuits can kill you!

Circuit Diagram Symbols

Circuit diagrams are used to illustrate the design of electrical circuits. These diagrams (often called “schematic diagrams” or just “schematics”) use symbols for various components rather than a drawing that closely resembles the actual appearance of the component. Switches, fuses, conductors, lights, etc., come in thousands of different sizes and shapes. The use of circuit symbols saves a lot of drawing time and space when designing a circuit. Some common circuit symbols are shown below.

The ratings in the following tabulation are those permitted by the National Electrical Code for flexible cords and for interior wiring of houses, hotels, office buildings, industrial plants, and other buildings.

The values are for copper wire. For aluminum wire the allowable carrying capacities shall be taken as 84% of those given in the table for the respective sizes of copper wire with the same kind of covering. (Source: Handbook of Chemistry & Physics, 74th Edition, 1993-94, pg. 15-29)

|Size |Diameter |Rubber |Varnished |Other |

|A.W.G. |of Solid |Insulation |Cabric |Insulations |

| |Wires Mils |Amperes |Insulation |and Bare |

| |(.001 inches) | |Amperes |Conductors |

| | | | |Amperes |

|18 |40.3 |3 * | |6** |

|16 |50.8 |6 * | |10** |

|14 |64.1 |15 |18 |20 |

|12 |80.8 |20 |25 |30 |

|10 |101.9 |25 |30 |35 |

|8 |128.5 |35 |40 |50 |

|6 |162.0 |50 |60 |70 |

|5 |181.9 |55 |65 |80 |

|4 |204.3 |70 |85 |90 |

|3 |229.4 |80 |95 |100 |

|2 |257.6 |90 |110 |125 |

|1 |289.3 |100 |120 |150 |

|0 |325.0 |125 |150 |200 |

|00 |364.8 |150 |180 |225 |

|000 |409.6 |175 |210 |275 |

* The allowable carrying capacities of No. 18 and 16 are 5 and 7 amperes respectively, when in flexible cords.

** The allowable carrying capacities of No. 18 and 16 are 10 and 15 amperes respectively, when in cords for portable heaters. Types AFS, AFSJ, HC, HPD, and HSJ.

Resistance in wire (values are for wire that is 1000 feet in length at 20oC.

|Gauge |Ohms per 1000 |Ohms per 1000 |Ohms per 1000 | |Gauge |Ohms per 1000 |Ohms per 1000 |Ohms per 1000 |

|No. |feet |feet |feet | |No. |feet |feet |feet |

| |@ 0oC |@ 20oC |@ 50oC | | |@ 0oC |@ 20oC |@ 50oC |

|10 |.9203 |.9989 |1.117 | |22 |14.87 |16.14 |18.05 |

|12 |1.463 |1.588 |1.775 | |24 |23.65 |25.65 |28.70 |

|14 |2.327 |2.525 |2.823 | |26 |37.61 |40.18 |45.63 |

|16 |3.700 |4.016 |4.489 | |28 |59.80 |64.90 |72.55 |

|18 |5.883 |6.385 |7.138 | |30 |95.08 |103.2 |115.4 |

|20 |9.355 |10.15 |11.35 | |32 |151.2 |164.1 |183.4 |

SUMMARY

Atoms are composed of these “subatomic particles”…

In the nucleus

- protons (+ charge)

- neutrons (no charge)

- and other smaller particles

Orbiting the nucleus in the electron cloud are the electrons ( - charge)

Atoms are electrically balanced or neutral because they have an equal number of protons and electrons.

When atoms become electrically unbalanced by the loss or gain of an electron they are called ions.

Particles with like charges repel each other.

Particles with unlike charges attract each other.

Electron flow - occurs when outer electrons of atoms are forced to jump to neighboring atoms either by repulsion or attraction.

Conductors - materials made of atoms, which have a weak attraction for their outer electrons. These materials have a low resistance to the flow of electricity.

Insulators - materials made of atoms, which have a strong attraction for their outer electrons. These materials have a high resistance to the flow of electricity.

Circuits – The two main classes of circuits are parallel and series. In a series circuit, the current flows first through one device and then through another. In a parallel circuit the current is split and goes simultaneously to two or more main devices.

A complete (unbroken or closed) circuit is one that has a continuous pathway for the electricity to travel from the source, through the devices and back to the source.

An incomplete (broken or open) circuit does not have a continuous pathway for the electricity from the source, through the devices and back to the source.

A short circuit bypasses the main electrical device(s) in a circuit. This is a dangerous form of complete circuit that allows the electricity to flow directly from the source through the wires and directly to the source without going through the intended device(s). Short circuits cause dangerous overheating of the wires and power source and may cause a fire or damage to the circuit.

Voltage - also called electrical potential , potential difference or electromotive force (EMF). Voltage is often thought of as "electrical pressure".

When voltage is increased more electrons move through the circuit over a given period of time.

The metric unit used to measure voltage is the volt. Two symbols are used for voltage.

- in electrical formulas E = volts

- in all other work V = volts

Current - the quantity of electrons flowing past a point during a given unit of time.

The metric unit used to measure current is the ampere (amp). 1 amp is equal to the passage of 6.24 x 1018 electrons in 1 second (1 coulomb/sec).

Two units are used to express current:

- in electrical formulas I = amperes (current)

- in all other electrical applications A = amperes

Direct Current

Electrons flow constantly in one direction.

Alternating Current

Electrons are forced to reverse their direction of travel many times per second.

Two reversals (alternations) equal one complete cycle.

A current that goes through one cycle each second is said to have a frequency of 1 Hz.

A current that undergoes more cycles per second than another current is said to have a higher frequency.

Resistance - all materials have some resistance to the flow of electrons because the positively charged nuclei of the atoms exert a holding force on the electrons, which opposes the voltage (electromotive force). This holding action results in a conversion of electrical energy into heat energy. All materials will undergo some “resistance heating” when subjected to electrical current. Some materials, like the wires in toasters, produce useful heat. In other materials, like the filaments in light bulbs and the wiring in transformers produce heat which is often wasted.

"Conductors" have less resistance than "insulators".

Resistance to electrical current causes heating of the conducting material.

The metric unit used to measure electrical resistance is the ohm. Resistance is expressed by two symbols:

- in formulas R= ohms (resistance)

- in most other electrical applications = ohm

More about conductors and insulators

All conductors have some resistance to the flow of electrons. The "perfect" conductor has not been discovered yet.

All insulators have a breakdown voltage at which electrons begin to flow. The "perfect" insulator has not been discovered yet.

Electrical components are rated according to the amount of voltage and current they can handle.

Ohm's Law

Ohm stated the relationship between voltage, current and resistance somewhat like this:

It takes 1 volt to push 1 amp through a resistance of 1 ohm.

or E=IR

Ohm's Law Formulas

The basic formula (E=IR) can be rewritten to solve for current and resistance as well as for voltage.

[pic] [pic]

To calculate the amps used by a device, use the formula

amps = I or A

voltage = E or V

watts = P or W

To calculate the watts used by a device, use the formula

-----------------------

Lithium - the simplest metallic atom.

This would be a “short circuit” and could ruin the battery, cause the battery to explode or cause the conductor to get hot enough to start a fire. You will learn more about circuits later.

I=

E

P

or

voltage

amps =

watts

watts =

volts

amps

CONDUCTORS MUST BE DRAWN AS STRAIGHT LINES OR STRAIGHT LINES WITH 90o TURNS.

Please use this electricity information packet to answer the questions on your electricity assignments. Do not use your book!

P = IE

or

X

2 conductors, crossing each other, but not electrically connected.

2 conductors that are electrically connected.

series

Heavy dots are

TERMINALS

-

+

A single cell - 1.5 volts

+

-

A 6 volt battery consisting of four 1.5 v cells

connected in series.

+

-

A 1.5 volt battery consisting of three 1.5 v cells connected in parallel.

parallel

A 2-terminal switch known as a SPST

(single pole, single throw)

“closed” position

“open” position

A 3-terminal switch known as a SPDT

(single pole, double throw)

“open” (off)

“closed” (on)

A fuse or circuit breaker.

An incandescent lamp (solid wire filament).

A diode.

A resistor.

A 1.5 volt battery - 4 cells in parallel

+

-

1.5 V

1.5 V

1.5 V

1.5 V

2-Cell Flashlight Circuit

(3 v)

_

+

1.5v

cell

_

+

1.5v

cell

“Complete Circuit”

(“Closed Circuit”)

(”On”)

_

+

1.5v

cell

“Incomplete Circuit”

(“Open Circuit”)

(”Off”)

_

+

1.5v

cell

Short Circuit

_

+

1.5v

cell

+

-

A complete circuit with a 3v battery, 3 lamps in parallel, a fuse and a switch in the closed position. Note that the fuse protects the entire circuit.

+

-

An incomplete circuit with a 3v battery, 2 lamps in series, a fuse and a switch in the open position.

+

-

A complete circuit with a 3v battery, a lamp, a fuse and a switch in the closed position.

+

-

A 6 volt battery - 4 cells in series

1.5 V

1.5 V

1.5 V

1.5 V

+

A 6 volt battery - 4 cells in series

A 6 volt battery - 4 cells in series

-

1.5 V

1.5 V

1.5 V

1.5 V

+

-

A 1.5 volt battery - 4 cells in parallel

+

-

Positive wires return electrons from the different devices to the battery.

In a truck (and other vehicles), only the positive side of the circuit is wire. The conductor for the negative side of the circuit is the metal frame and body of the truck.

-

+

Battery

Tail Light

Fuse Block

Dome Light

Light Switches

Cable from negative terminal bolted to the metal frame of the truck.

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