Unit 10 Competency 1 - Examine electrical systems in engineering

Suggested Objective a:  Differentiate between the concepts of “electricity” and “electronics”

 

 What is electricity?

We use electricity everyday. Without it we would not be able to watch t.v., listen to the radio, have hot water, use a microwave to heat our food and many of the other things we do every day.

But what is electricity?

First, you have to know what an atom is. An atom is the smallest part of something. It is microscopic, and every thing is made up of atoms. 

Atoms are made up of three parts. There are :

Protons These parts of an atom have a positive charge. They are in the middle of the atom, called the nucleus, and they do not move.

Neutrons - These parts of an atom have no charge. They are neutral and part of the nucleus of an atom with the protons.

Electrons - These parts of the atom are very small and weigh a lot less than the protons and neutrons. Electrons are not part of the nucleus of the atom, instead they move around in orbits outside the nucleus. Electrons are the only part of an atom that moves.

So what does this have to do with electricity?

Electricity is the flow of moving electrons. When the electrons flow, it is called an electrical current.

To understand why electrons flow, you need to understand that atoms can lose electrons by rubbing against another material. Think about when you rub your head against a balloon. Believe it or not, your hair is actually getting some electrons from the balloon. Because your hair has more electrons than protons, we say it is negatively charged.  But what about the balloon? Well, the balloon has more protons than electrons so it is positively charged.

Now that we know objects can have positive or negative charges, let's talk about how objects that are charged will behave. There are 3 main rules about electrical charges:

1. Like charges repel

So if both you and your friend rubbed balloons on your head and then tried to stick the balloons together, they would repel or push away from each other because they would both have the same charge.

2. Unlike charged objects attract - Since your hair has a positive charge and the balloon has a negative charge, they are attracted to each other. Kind of like magnets trying to stick together.

3. A charged object will attract an uncharged object -So, the balloon is charged; and the wall has no charge. This means the wall is attracted to the balloon.

Knowing these three rules, you can think of the lunch line full of boys. (Pretend the boys have a negative charge.)  A girl comes to the front of the line. (The girl has a positive charge.) The boys are attracted or trying to get as close as possible to the girl. The boys all start pushing the boy in front of him closer to the girl and to move away from the other boys. This is how the electrons flow. The negative charges (electrons) move because they are repelled by other electrons and because they are attracted to the positive charges (protons).

The flowing electrons make electricity, but how can we use it?

You need three things to let you use this electrical current: a circuit or a path for the electrons to move through, a power source, or something that is going to make the electrons move, like a battery or a generator, and something to use the electricity, like a light bulb or a t.v..

The power source causes the electrical current that goes through a circuit or a closed path, and the appliance is connected to the circuit so the electrons can move through it and make the appliance work.

 

The above information was copied from http://www.edu.pe.ca/kish/Grassroots/Elect/whatis.htm Links to an external site. on December 2, 2014.

 

Definition of electronics: Electronics is the branch of science that deals with the study of flow and control of electrons (electricity) and the study of their behavior and effects in vacuums, gases, and semiconductors, and with devices using such electrons. This control of electrons is accomplished by devices that resist, carry, select, steer, switch, store, manipulate, and exploit the electron.

Some of the basic electrical units and definitions are mentioned below:

Passive: Capable of operating without an external power source. Typical passive components are resistors, capacitors, inductors and diodes (although the latter are a special case).

Active: Requiring a source of power to operate.    Includes transistors (all types), integrated circuits (all types), TRIACs, SCRs, LEDs, etc.

DC: Direct Current. The electrons flow in one direction only.  Current flow is from negative to positive, although it is often more convenient to think of it as from positive to negative.  This is sometimes referred to as "conventional" current as opposed to electron flow.

 

AC: Alternating Current. The electrons flow in both directions in a cyclic manner - first one way, then the other.  The rate of change of direction determines the frequency, measured in Hertz (cycles per second).

 

Frequency: Unit is Hertz, Symbol is Hz, old symbol was cps (cycles per second). A complete cycle is completed when the AC signal has gone from zero volts to one extreme, back through zero volts to the opposite extreme, and returned to zero.  The accepted audio range is from 20Hz to 20,000Hz.  The number of times the signal completes a complete cycle in one second is the frequency.

 

Voltage: Unit is Volts, Symbol is V or U, old symbol was E . Voltage is the "pressure" of electricity, or "electromotive force" (hence the old term E).  A 9V battery has a voltage of 9V DC, and may be positive or negative depending on the terminal that is used as the reference.  The mains has a voltage of 220, 240 or 110V depending where you live - this is AC, and alternates between positive and negative values.  Voltage is also commonly measured in millivolts (mV), and 1,000 mV is 1V.  Microvolts (uV) and nanovolts (nV) are also used.

 

Current: Unit is Amperes (Amps), Symbol is I . Current is the flow of electricity (electrons).  No current flows between the terminals of a battery or other voltage supply unless a load is connected.  The magnitude of the current is determined by the available voltage, and the resistance (or impedance) of the load and the power source.  Current can be AC or DC, positive or negative, depending upon the reference.  For electronics, current may also be measured in mA (milliamps) - 1,000 mA is 1A.  Nanoamps (nA) are also used in some cases.

 

Resistance: Unit is Ohms, Symbol is R or Ω . Resistance is a measure of how easily (or with what difficulty) electrons will flow through the device.  Copper wire has a very low resistance, so a small voltage will allow a large current to flow.  Likewise, the plastic insulation has a very high resistance, and prevents current from flowing from one wire to those adjacent.  Resistors have a defined resistance, so the current can be calculated for any voltage.  Resistance in passive devices is always positive (i.e. > 0)

Information above was copied from http://www.electronicsandyou.com/electronics-basics/electronics_definitions.html Links to an external site. on December 2, 2014.

 

 

Please see this link for a Quizlet associated with the terms you will need to be familiar with: Electricity Vocabulary Links to an external site.

Please see this video Links to an external site. for a quick review of binary numbers.

 

Suggested Objective b:  Identify the following electrical components: resistor, capacitor, transistor, breadboard, multimeter

 

A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.

All other factors being equal, in a direct-current (DC) circuit, the current through a resistor is inversely proportional to its resistance, and directly proportional to the voltage across it. This is the well-known Ohm's Law. In alternating-current (AC Links to an external site.) circuits, this rule also applies as long as the resistor does not contain inductance or capacitance.

Resistors can be fabricated in a variety of ways. The most common type in electronic devices and systems is the carbon-composition resistor. Fine granulated carbon (graphite) is mixed with clay and hardened. The resistance depends on the proportion of carbon to clay; the higher this ratio, the lower the resistance.

Another type of resistor is made from winding Nichrome or similar wire on an insulating form. This component, called a wirewound resistor, is able to handle higher currents than a carbon-composition resistor of the same physical size. However, because the wire is wound into a coil, the component acts as an inductors as well as exhibiting resistance. This does not affect performance in DC circuits, but can have an adverse effect in AC circuits because inductance renders the device sensitive to changes in frequency.

Information copied from http://whatis.techtarget.com/definition/resistor Links to an external site. on December 8, 2014

What Is a Resistor? Links to an external site.

Why Are Capacitors Important?

       The capacitor is a widely used electrical component.  It has several features that make it useful and important:

• A capacitor can store energy, so capacitors are often found in power supplies.
• A capacitor has a voltage that is proportional to the charge (the integral of the current) that is stored in the capacitor, so a capacitor can be used to perform interesting computations in op-amp circuits, for example.
• Circuits with capacitors exhibit frequency-dependent behavior so that circuits that amplify certain frequencies selectively can be built.

---

What Is A Capacitor?

        Capacitors are two-terminal electrical elements.  Capacitors are essentially two conductors, usually conduction plates - but any two conductors - separated by an insulator - a dielectric - with connection wires connected to the two conducting plates.

        Capacitors occur naturally. On printed circuit boards two wires running parallel to each other on opposite sides of the board form a capacitor. That's a capacitor that comes about inadvertently, and we would normally prefer that it not be there. But, it's there.  It has electrical effects, and it will affect your circuit.  You need to understand what it does.

        At other times, you specifically want to use capacitors because of their frequency dependent behavior. There are lots of situations where we want to design for some specific frequency dependent behavior. Maybe you want to filter out some high frequency noise from a lower frequency signal. Maybe you want to filter out power supply frequencies in a signal running near a 60 Hz line. You're almost certainly going to use a circuit with a capacitor.

        Sometimes you can use a capacitor to store energy.  In a subway car, an insulator at a track switch may cut off power from the car for a few feet along the line. You might use a large capacitor to store energy to drive the subway car through the insulator in the power feed.

        Capacitors are used for all these purposes, and more. In this chapter you're going to start learning about this important electrical component. Remember capacitors do the following and more.

• Store energy
• Change their behavior with frequency
• Come about naturally in circuits and can change a circuit's behavior

Information copied from http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/LC/Capac1.htm Links to an external site. on December 8, 2014

What Is a Capacitor? Links to an external site.

 

Transistors are tiny switches that can be triggered by electric signals. They are the basic building blocks of microchips, and roughly define the difference between electric andelectronic devices.

How does a transistor work?

A traditional mechanical switch either enables or disables the flow of electricity by physically connecting (or disconnecting) two ends of wire. In a transistor, a signal tells the device to either conduct or insulate, thereby enabling or disabling the flow of electricity. This property of acting like an insulator in some circumstances and like a conductor in others is unique to a special class of materials known as “semiconductors.”

Information copied from http://www.livescience.com/46021-what-is-a-transistor.html Links to an external site. on December 8, 2014

What Is a Transistor?  How Does a Transistor Work?  Part 1 Links to an external site.

What Is a Transistor?  How Does a Transistor Work?  Part 2 Links to an external site.

A breadboard is a rectangular plastic box filled with holes, which have contacts in which you can insert electronic components and wires. A breadboard is what you use to string together a temporary version of your circuit. You don't have to solder wires or anything else; instead, you poke your components and wires into the little contact holes arranged in rows and connected by lines of metal; then you can connect your components together with wires to form your circuit.

The nice thing about breadboards is that you can change your mind and replace or rearrange components as you like. You typically create an electronics project on a breadboard to make sure that everything works. If it's a project you wish to save, you can create a more permanent version.

When you place components in a breadboard, you don't get much action until you connect those components with wire. Wire used in electronics is copper surrounded by a plastic insulator, usually called hookup wire. Hookup wire comes in various diameters referred to as a gauge. The standard gauge measurement used in the U.S. is American Wire Gauge, also referred to as AWG.

Someone decided at some point that the smaller the gauge, the larger the diameter of wire. For example, 20 gauge wire is 0.032" in diameter, and 22 gauge wire is 0.025" in diameter. Don't ask why — just memorize this fact!

Use solid wire — never stranded wire — between components within a breadboard because stranded tends to separate when you try to insert it into the holes of a breadboard.

Information copied from http://www.dummies.com/how-to/content/electronics-basics-using-a-breadboard.html Links to an external site. on December 8, 2014

How To:  The Basics of Breadboarding Links to an external site.

How to Use Breadboard - Using Breadboard for Beginners and Prototyping Circuits Links to an external site.

What is a multimeter?

A multimeter is a handy tool that you use to measure electricity, just like you would use a ruler to measure distance, a stopwatch to measure time, or a scale to measure weight. The neat thing about a multimeter is that unlike a ruler, watch, or scale, it can measure different things — kind of like a multi-tool. Most multimeters have a knob on the front that lets you select what you want to measure. Below is a picture of a typical multimeter. There are many different multimeter models; visit the multimeter gallery Links to an external site. for labeled pictures of additional models.

What can multimeters measure?

Almost all multimeters can measure voltage, current, and resistance. See the next section Links to an external site. for an explanation of what these terms mean, and click on the Using a Multimeter Links to an external site. tab, above, for instructions on how to make these measurements.

Some multimeters have a continuity check, resulting in a loud beep if two things are electrically connected. This is helpful if, for instance, you are building a circuit and connecting wires or soldering; the beep indicates everything is connected and nothing has come loose. You can also use it to make sure two things arenot connected, to help prevent short circuits.

Some multimeters also have a diode check function. A diode is like a one-way valve that only lets electricity flow in one direction. The exact function of the diode check can vary from multimeter to multimeter. If you're working with a diode and can't tell which way it goes in the circuit, or if you're not sure the diode is working properly, the check feature can be quite handy. If your multimeter has a diode check function, read the manual to find out exactly how it works.

Advanced multimeters might have other functions, such as the ability to measure and identify other electrical components, like transistors or capacitors. Since not all multimeters have these features, we will not cover them in this tutorial. You can read your multimeter's manual if you need to use these features.

What are voltage, current, and resistance?

If you haven't heard of these terms before, we'll give a very simple introductory explanation here. You can read more about voltage, current, and resistance in theReferences Links to an external site. tab, above. Remember that voltage, current, and resistance are measurable quantities that are each measured in a unit that has a symbol, just like distance is a quantity that can be measured in meters, and the symbol for meters is m.

• Voltage is how hard electricity is being "pushed" through a circuit. A higher voltage means the electricity is being pushed harder. Voltage is measured involts. The symbol for volts is V.
• Current is how much electricity is flowing through the circuit. A higher current means more electricity is flowing. Current is measured in amperes. The symbol for amperes is A.
• Resistance is how difficult it is for electricity to flow through something. A higher resistance means it is more difficult for electricity to flow. Resistance is measured in ohms. The symbol for ohms is Ω (the capital Greek letter omega).

Information copied from http://www.sciencebuddies.org/science-fair-projects/multimeters-tutorial.shtml Links to an external site. on December 8, 2014

THE BEST Multimeter Tutorial (HD) Links to an external site.

Suggested Objective c:  Identify different types of electricity

 

There are two types of Electricity, Static Electricity and Current Electricity. Static Electricity is made by rubbing together two or more objects and making friction while Current electricity is the flow of electric charge across an electrical field.

Static Electricity

Static electricity is when electrical charges build up on the surface of a material. It is usually caused by rubbing materials together. The result of a build-up of static electricity is that objects may be attracted to each other or may even cause a spark to jump from one to the other. For Example rub a baloon on a wool and hold it up to the wall.

Before rubbing, like all materials, the balloons and the wool sweater have a neutral charge. This is because they each have an equal number of positively charged subatomic particles (protons) and negatively charged subatomic particles (electrons). When you rub the balloon with the wool sweater, electrons are transferred from the wool to the rubber because of differences in the attraction of the two materials for electrons. The balloon becomes negatively charged because it gains electrons from the wool, and the wool becomes positively charged because it loses electrons.

Current Electricity

Current is the rate of flow of electrons. It is produced by moving electrons and it is measured in amperes. Unlike static electricity, current electricity must flow through a conductor, usually copper wire. Current with electricity is just like current when you think of a river. The river flows from one spot to another, and the speed it moves is the speed of the current. With electricity, current is a measure of the amount of energy transferred over a period of time. That energy is called a flow of electrons. One of the results of current is the heating of the conductor. When an electric stove heats up, it's because of the flow of current.

There are different sources of current electricity including the chemical reactions taking place in a battery. The most common source is the generator. A simple generator produces electricity when a coil of copper turns inside a magnetic field. In a power plant, electromagnets spinning inside many coils of copper wire generate vast quantities of current electricity.

There are two main kinds of electric current. Direct (DC) and Alternating (AC). It's easy to remember. Direct current is like the energy you get from a battery. Alternating current is like the plugs in the wall. The big difference between the two is that DC is a flow of energy while AC can turn on and off. AC reverses the direction of the electrons.

Information copied from http://www.electricityforum.com/types-electricity.html Links to an external site.on December 8, 2014

Other great sites with information for electricity -

http://www.explainthatstuff.com/electricity.html Links to an external site.

http://www.enwin.com/kids/electricity/types_of_energy.cfm Links to an external site.

http://www.solarpowernotes.com/electricity/types-of-electricity.html#.VIYhZTHF98E Links to an external site.

 

Suggested Objective d:  Describe conductors, semiconductors, and insulators

 

The behavior of an object that has been charged is dependent upon whether the object is made of a conductive or a nonconductive material. Conductors are materials that permit electrons to flow freely from particle to particle. An object made of a conducting material will permit charge to be transferred across the entire surface of the object. If charge is transferred to the object at a given location, that charge is quickly distributed across the entire surface of the object. The distribution of charge is the result of electron movement. Since conductors allow for electrons to be transported from particle to particle, a charged object will always distribute its charge until the overall repulsive forces between excess electrons is minimized. If a charged conductor is touched to another object, the conductor can even transfer its charge to that object. The transfer of charge between objects occurs more readily if the second object is made of a conducting material. Conductors allow for charge transfer through the free movement of electrons.

 

In contrast to conductors, insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. The particles of the insulator do not permit the free flow of electrons; subsequently charge is seldom distributed evenly across the surface of an insulator.

While insulators are not useful for transferring charge, they do serve a critical role in electrostatic experiments and demonstrations. Conductive objects are often mounted upon insulating objects. This arrangement of a conductor on top of an insulator prevents charge from being transferred from the conductive object to its surroundings. This arrangement also allows for a student (or teacher) to manipulate a conducting object without touching it. The insulator serves as a handle for moving the conductor around on top of a lab table. If charging experiments are performed with aluminum pop cans, then the cans should be mounted on top of Styrofoam cups. The cups serve as insulators, preventing the pop cans from discharging their charge. The cups also serve as handles when it becomes necessary to move the cans around on the table.

 

Examples of Conductors and Insulators

Examples of conductors include metals, aqueous solutions of salts (i.e., ionic compounds dissolved in water), graphite, and the human body. Examples of insulators include plastics, Styrofoam, paper, rubber, glass and dry air. The division of materials into the categories of conductors and insulators is a somewhat artificial division. It is more appropriate to think of materials as being placed somewhere along a continuum. Those materials that are super conductive (known as superconductors) would be placed at on end and the least conductive materials (best insulators) would be placed at the other end. Metals would be placed near the most conductive end and glass would be placed on the opposite end of the continuum. The conductivity of a metal might be as much as a million trillion times greater than that of glass.

 

Along the continuum of conductors and insulators, one might find the human body somewhere towards the conducting side of the middle. When the body acquires a static charge it has a tendency to distribute that charge throughout the surface of the body. Given the size of the human body, relative to the size of typical objects used in electrostatic experiments, it would require an abnormally large quantity of excess charge before its effect is noticeable. The effects of excess charge on the body are often demonstrated using a Van de Graaff generator. When a student places their hand upon the static ball, excess charge from the ball is shared with the human body. Being a conductor, the excess charge could flow to the human body and spread throughout the surface of the body, even onto strands of hair. As the individual strands of hair become charged, they begin to repel each other. Looking to distance themselves from their like-charged neighbors, the strands of hair begin to rise upward and outward - a truly hair-raising experience.

Many are familiar with the impact that humidity can have upon static charge buildups. You have likely noticed that bad hair days, doorknob shocks and static clothing are most common during winter months. Winter months tend to be the driest months of the year with humidity levels in the air dropping to lower values. Water has a tendency to gradually remove excess charge from objects. When the humidity is high, a person acquiring an excess charge will tend to lose that charge to water molecules in the surrounding air. On the other hand, dry air conditions are more conducive to the buildup of static charge and more frequent electric shocks. Since humidity levels tend to vary from day to day and season to season, it is expected that electrical effects (and even the success of electrostatic demonstrations) can vary from day to day.

Information copied from http://www.physicsclassroom.com/class/estatics/Lesson-1/Conductors-and-Insulators Links to an external site. on December 8, 2014

Insulators and Conductors:  Examples, Definitions, and Qualities Links to an external site. (this site has a video and quiz to help you learn about insulators and conductors)

Insulator versus Conductor Links to an external site.

 

Suggested Objective e:  Describe an electric circuit

 

 

You might have been wondering how electrons can continuously flow in a uniform direction through wires without the benefit of these hypothetical electron Sources and Destinations. In order for the Source-and-Destination scheme to work, both would have to have an infinite capacity for electrons in order to sustain a continuous flow! Using the marble-and-tube analogy, the marble source and marble destination buckets would have to be infinitely large to contain enough marble capacity for a "flow" of marbles to be sustained.

The answer to this paradox is found in the concept of a circuit: a never-ending looped pathway for electrons. If we take a wire, or many wires joined end-to-end, and loop it around so that it forms a continuous pathway, we have the means to support a uniform flow of electrons without having to resort to infinite Sources and Destinations:

Each electron advancing clockwise in this circuit pushes on the one in front of it, which pushes on the one in front of it, and so on, and so on, just like a hula-hoop filled with marbles. Now, we have the capability of supporting a continuous flow of electrons indefinitely without the need for infinite electron supplies and dumps. All we need to maintain this flow is a continuous means of motivation for those electrons, which we'll address in the next section of this chapter.

It must be realized that continuity is just as important in a circuit as it is in a straight piece of wire. Just as in the example with the straight piece of wire between the electron Source and Destination, any break in this circuit will prevent electrons from flowing through it:

An important principle to realize here is that it doesn't matter where the break occurs. Any discontinuity in the circuit will prevent electron flow throughout the entire circuit. Unless there is a continuous, unbroken loop of conductive material for electrons to flow through, a sustained flow simply cannot be maintained.

Information copied from http://www.allaboutcircuits.com/vol_1/chpt_1/3.html Links to an external site. on December 8, 2014

 

Explaining an Electrical Circuit Links to an external site.

 

Suggested Objective f:  Distinguish between parallel and series circuits

 

Image copied from http://www.ia470.com/primer/electric.htm Links to an external site. on December 8, 2014

Information copied from https://learn.sparkfun.com/tutorials/series-and-parallel-circuits Links to an external site. on December 8, 2014

Parallel and Series Circuits Links to an external site.