February 2011DRILL

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It uses direct current because it is powered by a battery. If

it used alternating current you would be able to plug

it into a wall outlet. We will find out more about

AC and DC current in this unit.

•Write the question and circle the answer you think is

correct . Next, write why?

What kind of power source do you think provides the proper

current for this shaver to work?

A) AC (Alternating Current)

B) DC (Direct Current)

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UNIT 3 – Engineering Design

a. Getting familiar with the Big Idea

b. The Design Process

c. Core Technologies

d. Mechanical Technology

e. Electrical Technologyf. Reverse Technology

g. Fluid Technology

h. Thermal Technology

i. Optical Technology

j. Materials Technology

Electrical Technology

PURPOSE OF SUB-UNIT

• To familiarize students with the functioning and applications of electrical technology systems by having you analyze the functioning of electrical systems in terms of their:– common components, – basic system design, – safety considerations, and – simple controls. U3e-L1

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• A technology system is a group of resources (subsystems) working together to solve problems and extend human capabilities.– What subsystems make up this system?

• Identify the problem that the technology system solves.

• Speculate on how the device assists people in solving a problem or extending human capability.

What is this technology system?

Definition:

The technology of using small amounts of electricity for controlling, detecting, collecting, storing, retrieving and processing information.

Applications:

Thermostat, metal detector,video recorder, computer,calculator, telephone,television, radio, pace maker, digital watch. U3e-L1

Definition:

The technology of producing, storing, controlling,transmitting and getting work from electrical energy.

Applications:

Power plant generator, flashlight, electric motor in a can opener, doorbell, electric heater, hair dryer. U3e-L1

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Electrical Technology

• Electricity completely surrounds us.• For most of us, modern life would be impossible

without it.• Examples:

– Electrical outlets along walls in your house/school– Portable devices (cell phones, ipods, calculators)

powered by batteries– Bolts of electricity (lightning) during thunderstorms– Static electricity on dry winter days– Solar cells converting the sun’s energy into

electricity

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• Electricity can be used in a thousand different ways. For example: – Electric motors turn electricity into motion. – Light bulbs, fluorescent lamps and LEDs turn

electricity into light. – Computers turn electricity into information. – Telephones turn electricity into communication. – TVs turn electricity into moving pictures. – Speakers turn electricity into sound waves. – Stun guns turn electricity into pain. – Toasters, hair dryers and space heaters turn

electricity into heat. – Radios turn electricity into electromagnetic waves that

can travel millions of miles. – X-ray machines turn electricity into X-rays.

Electrical Technology

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ELECTRONS

• Electricity begins with Electrons.

ATOMS• Electron cloud surrounds an

atom’s nucleus• Nucleus is made of

• Electrons – negative charge• Protons – positive charge• Neutrons – zero charge (neutral)

Protons and Neutrons

Pity the poor neutron;he thought he was a

protonbut he wasn’t positive.

• Electric Charge and Electrical Forces:

• Electrons have a negative electrical charge.

• Protons have a positive electrical charge.

• These charges interact to create an electrical force.

– Like charges produce repulsive forces – so they repel each other (e.g. electron and electron or proton and proton repel each other).

– Unlike charges produce attractive forces – so they attract each other (e.g. electron and proton attract each other).

All of us agree the importance of electricity in our daily lives.

But what is electricity?

• Electricity is a basic feature of all matter, of everything in the universe. Electrical force holds atoms and molecules together. Electricity determines the structure of every object that exists. Together with magnetism, it causes a force called electromagnetism, a fundamental force of the universe.

•  

• Electricity or electrical signals are essential to many biological processes. In our bodies, electrical signals are carried through the nervous system, moving information to and from the brain. Electrical signals communicate to our brain what the eyes see, what the ears hear, and what the fingers feel. Electrical signals from our brain causes our muscle movements. Electrical signals cause each heartbeat.

•  

• One of the most important forms of electricity is in electrical current. During the industrial revolution of the 1800s, people began to find ways to use electricity to do work. Today electricity is used throughout our homes, at work, in communication, in transportation, and in medicine and science. Electrically powered devices are prevalent. Relatively cheap electricity has made electrical appliances, machines, and other devices possible.

•  

What is static electricity?

When two objects rub against each other electrons transfer and build up on an object causing it to have a different charge from its surroundings.

Like the shoes rubbing against the carpet. Electrons are transferred from the carpet to the shoes.

As electrons collect on an object, it becomes negatively charged. As electrons leave an object it attains a positive charges. Charges interact with each other:

Often when you remove clothes from the clothes dryer, they seem to stick together. This is because some of the clothes have gained electrons by rubbing against other clothes. The clothes losing electrons become positive. The negative clothes are attracted to the positive clothes.

Have you ever rubbed a balloon on your hair and stuck it on a wall? How do you think this works?

What causes you to be shocked when you rub your feet across carpet?

An electrical discharge is the passing of an electric current through the air from a negatively charged object to a positively charge object. This is what causes lightning!

Arbitrary numbers of protons (+) and electrons (-) on a comb and in hair (A) before and (B) after combing. Combing transfers electrons from the hair to the comb by friction, resulting in a negative charge on the comb and a positive charge on the hair.

• The charge on an ion is called an electrostatic charge.

• An object becomes electrostatically charged by–Friction,which transfers electrons between

two objects in contact,

–Contact with a charged body which results in the transfer of electrons,

– Induction which produces a charge redistribution of electrons in a material.

Charging by induction: The comb has become charged by friction, acquiring an excess of electrons. The paper (A) normally has a random distribution of (+) and (-) charges. (B) When the charged comb is held close to the paper, there is a reorientation of charges because of the repulsion of the charges. This leaves a net positive charge on the side close to the comb, and since unlike charges attract, the paper is attracted to the comb.

Lightning (1)

1. Identify 5 electrical technologies not mentioned in class today

• (Remember, an electrical technology produces, stores, controls, transmits or gets work from electrical energy)

2. Identify the problem that the technology system solves

3. List the technological subsystems that are used in the technology

4. Identify the technology that preceded it (i.e. what was used before the technology was invented?)

EXTRA CREDIT: Air is an insulator. Come to class tomorrow and explain how lightning happens.

February 2011DRILL

1. What are the three methods an object can become electrostatic?

2. What are three components of an atom?

3. What are the charges of each component?

4. Which component is the basis for electricity?

February 9, 2011DRILL

1. What are the three methods an object can become electrostatic? Friction, Contact, Induction

2. What are three components of an atom? Electrons, Protons, and Neutrons

3. What are the charges of each component? Electrons-negative, Protons-positive, and Neutrons-neutral

4. Which component is the basis for electricity? Electrons

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1. Identify 5 electrical technologies not mentioned in class today

• (Remember, an electrical technology produces, stores, controls, transmits or gets work from electrical energy)

2. Identify the problem that the technology system solves

3. List the technological subsystems that are used in the technology

4. Identify the technology that preceded it (i.e. what was used before the technology was invented?)

EXTRA CREDIT: Air is an insulator. Come to class tomorrow and explain how lightning happens.

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LOAD

• Power Source – with positive and negative terminals.

• Conductor – the path the electrons travel along.

• Load – this is what the electricity powers (e.g. motor, light bulb)

CIRCUITS

• The paths that electrons travel are called circuits.• Circuits must consist of three things:

ELECTRONS move from negative ( - )

terminal to positive ( + )

terminal

What is the difference between static electricity and current electricity?

Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor.

The flow of electricity in current electricity has electrical pressure or voltage. Electric charges flow from an area of high voltage to an area of low voltage.

Water pressure and voltage behave in similar ways.

• Moving electrons have energy.

• Electrons moving through a wire (conductor) in a circuit have energy.

• As the electrons move from one point to another, they can do work.

• Electrical Technology harnesses the energy of electrons to do work.

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CIRCUITS

A simple electric circuit has a voltage source (such as a generator or battery) that maintains the electrical potential, some device (such as a lamp or motor ) where work is done by the potential, and continuous pathways for the current to follow.

• The Electric Circuit:An electrical circuit contains some device that acts as a source of energy as it gives charges a higher potential against an electrical field.

• The charges do work as they flow through the circuit to a lower potential.

• The charges flow through connecting wires to make a continuous path.

• A switch is a means of interrupting or completing the circuit.

– The source of the electrical potential is the voltage source.

The pressure of the water flowing through the pipes on the last slide compare to the voltage (electric potential) flowing through the wires of the circuit. The unit used to measure voltage is volts (V).

The flow of charges in a circuit is called current. Current (I) is measured in Amperes (A).

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CONDUCTORS

• Conduct – from Latin for “leading, guiding.” • A conductor is any material that allows electrons

to easily flow.• Remember the atom:

– Conductors’ electrons are not tightly bound to the atom.– Conductors have free electrons.

• Which material has free electrons, Wood or Metal?

• Metals conduct electricity easily.

(A) A metal conductor without a current has immovable positive ions surrounded by a swarm of randomly moving electrons.

(B) An electric field causes the electrons to shift positions, creating a separation charge as the electrons move with a zigzag motion from collisions with stationary positive ions and other electrons.

The four factors that influence the resistance of an electrical conductor are the length of the conductor, the cross-sectional area of the conductor, the material the conductor is made of, and the temperature of the conductor.

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• Insulate – from Latin for “separate, divided.”

• An insulator is any material that impedes the flow of electrons.

• Remember the atom:– Insulators’ electrons are tightly bound to the atom. – Because the electrons don’t move, insulators cannot

conduct electricity very well, if at all.

• Which material has bound electrons, Wood or Metal?

• Wood does not have free electrons.

INSULATORS

CottonBound ElectronsGoldWoodPlasticSilverAluminumAirCopperFree-electrons

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INSULATORCotton

Wood

Plastic

Air

BOUND ELECTRONS

CONDUCTORCopper

Gold

Silver

Aluminum

FREE ELECTRONS

1. List 5 electrical devices you absolutely need and why.

2. List 5 electrical devices you do not need.