electrical principles and technologies - wordpress.com · electrical principles and technologies...

2016-02-17

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ELECTRICAL PRINCIPLES

AND TECHNOLOGIES

Science 9 Unit D

Science 9 Unit D Section 1.0 1

1.1 Static Electricity

1.0 Electrical energy can be transferred

and stored.

Tesla C

oil

Science 9 Unit D Section 1.0

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Junior Electrician: Static Electricity (14:38)


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1. What is Static Electricity?


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Static Electricity is a stationary electric charge

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2. How does an object become neutral?

Most objects have equal

amounts of (+) and (–)

charges, which makes them

neutral.

While protons and neutrons

are fixed in the nucleus of

the atom, electrons orbit the

nucleus and are free to be

removed.

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e-

e- e-

e-

e-

e-

*Neutral*

description of an object that has equal amounts of

positive and negative charges

+ ―

+ ―

+ ―

+ ―

+ ―

+ ―


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3. What does the word ‘static’ mean?

“Static” means “not moving” or “stationary.” This

type of charge does not flow like the electrons in

an electrical current.


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Recall: *Electrical Charge*

An object with more electrons

than protons is negatively

charged.

When this happens, we say

that an object has built up a

static charge.

e-

e- e-

e-

e-

Natural static discharge


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4. The Laws of Electrical Charges

Opposite charges attract each other.

Like charges repel each other.

Figure 1.2 – pg. 276


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http://en.wikipedia.org/wiki/File:Lightning_strike_jan_2007.jpg

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Static Electricity


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5. What causes charge separation?

Bringing charged objects close to neutral objects and friction! (Rubbing two objects together)

Example: Rubbing a balloon on your head transfers electrons from your hair to the balloon.

The negative charge of the balloon repels the electrons in the wall, which leaves the area of the wall closest to the balloon positive.

The balloon is attracted to the wall.


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_

_

_

_

_

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6. What is an Electrical Discharge?

Static electricity does not flow like a current.

The built-up charge on an object may be attracted to another object and jump to that object; that is, electrons transfer to other objects.

Electrical discharge is the sudden transfer of electrical charge from one object to another, indicated by a spark, which makes the object neutral.


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7. Van de Graaff Generator (VDG)

VDGs produce static build-up by using friction.

A rubber belt rubs on a piece of metal and

transfers the charge to a sphere.

The charge builds up on the sphere and transfers to

you when you touch the sphere.


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Bill Nye is an Expert on This Subject!


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8. You rub your feet across a floor and electrons transfer from

you to the floor. Are you now negatively or positively

charged?

If electrons transfer

from you to the floor,

that means that you

have lost electrons,

which means you are

left with a positive

charge.

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9. A neutral object contains no charge.

Is this statement accurate? Explain.


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This statement is mostly accurate. A neutral object

contains a bunch of zero pairs; that is, equal

numbers of positive and negative charges that

balance with each other so there is no overall

charge.

10. Why is a neutral object attracted to a

charged object?


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A charged object will cause charge separation in a

neutral object. For example, the negative charges in

the neutral object will move away from an

approaching negative object, leaving a positive

area. This positive area will be attracted to the

negative approaching object.

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11. Large trucks that carry flammable liquids often have a

metal wire or chain that drags on the ground. Why?


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Large trucks can acquire a large negative charge due to friction with the air. When these negative charges discharge, they can ignite flammable liquids, leading to dangerous fires and explosions.

The metal wire touching the ground allows the electrons to continually discharge, so no dangerous static charge builds up.

Neutral metal sphere

― + ― + ― + ― + ― + ― +

― ― ― ― ― ―

+ + + + + +

Temporary charging

by induction

+ + + + + +

Ground

― ― ― ― ― ―

Permanent charging

by induction

+ + + + + +

Positively charged

metal sphere


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Some safety precautions...


Homework!

Read Textbook

Pages 279 – 283

Key Terms

Topic 1.2

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Unit A - Section 1.0

http://www.flickr.com/photos/saroy/4096098591/

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1.2 Current Electricity


and stored.

Did You Know? Electric Eel (Electrophorous electricus)

Produces a static charge which can be discharged to stun or kill its prey when it flows

The average discharge is more than 350 volts.

Some South American eels measure 10 feet in length.

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1. Why are static charges not useful

for operating electrical devices?

Static charges are not useful for operating electrical

devices because static charges build up and

discharge, but they do not flow continuously.

Electrical devices require a constant flow of

electrons.

2. What is an Electrical Current?

Electrical current is the steady and continuous flow

of charged particles.

This is the type of electricity needed to operate

electrical devices.

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3. What two conditions must be met for

an electrical current to flow continuously?

1. The flow of electrical

current requires an

energy source.

2. Electrical current will

not flow unless it has a

complete path or

*circuit* for the

charged particles to

flow through.

4. What do Amperes (A) measure?

The rate at which an electric current flows is

measured in amperes (A), often called amp for

short.

Large currents are measured with an ammeter.

Rate means: how fast is it flowing?

^Named after André-Marie Ampère, one of the

main discoverers of electromagnetism.^

^Think of a river flowing – when we talk about the

current, we’re asking how fast is the water flowing? It’s

the same idea in electricity, except instead of water

flowing, it’s an electric current!^

http://en.wikipedia.org/wiki/Image:Ampere1.jpg

http://en.wikipedia.org/wiki/Andr%C3%A9-Marie_Amp%C3%A8re



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Current in amps of

Common Electrical Devices

60-W light bulb = 15 A

Microwave Oven = 5 – 8 A

Electric Kettle = 13 A

Television = 4 – 5 A

Ceiling Fan = 4 A

5. What are conductors?

Conductors are materials that electrical charges can

easily move through.

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6. What does the conduction of

electricity through wires allow for?

Conduction of electricity through wires allows for the

transfer of electrical energy from place to place.

Pg. 280

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7. What is a circuit?

A circuit is a path that controls the flow of electricity.

Made up of solid metal wires, but can include

gases, other fluids, or other substances.

8. What are the four main circuit

components?

Usually consists of:

1. a power switch

2. a conductor

A conductor is a material that will let electrons flow (i.e. most

metals)

3. an energy source (power supply)

4. a load

The *load* is a device to convert electrical energy to

another form of energy (i.e. a light bulb).

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9. How are electrical energy and

voltage related?

Electrical energy is the energy carried by charged

particles. How much electrical energy each charged

particle carries is the voltage.

Electrical energy is transferred when electrons travel

from place to place.

10. & 11. Voltage = Potential Difference

The higher the voltage is, the greater the potential

energy of each particle.

In other words:

↑ voltage = ↑ potential energy of each particle

Voltage is also called “potential difference.”

Potential means “the ability to do work.”

Energy delivered = Voltage x Total charge of electrons

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Potential Difference

12. What is the unit of voltage?

The unit of voltage is the volt (V).

For your safety, most voltages in everyday devices

are fairly low.

Flashlights = 6 V

Home/school sockets = 120 V

Industrial machinery = 600 V

^Named after Alessandro Volta; an Italian physicist

known especially for the development of the electric

battery in 1800 ^

http://en.wikipedia.org/wiki/Image:Alex_volta.jpg

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13. How can voltage be measured?

A voltmeter is an instrument for measuring potential difference (Voltage) in volts.

Red (+), Black (–)

Some meters may give readings in millivolts (mV).

i.e. 40 mV = 0.040 V

14. How does current electricity differ

from static electricity?


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Static charges build up and discharge, but they do

not flow continuously.

Electrical currents flow continuously, as long as there

is an energy source and a complete path or circuit

for the particles to flow through.

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15. What is the reading on the

voltmeter in the figure to the right:

a. In mV?

15.5 mV

b. In V?

15.5 ÷ 1000

0.0155 V

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Homework!

Read Textbook

Pages 284 – 287

Key Terms

Topic 1.3

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1.3 Electrical Safety


and stored.

1. What is a short circuit?

An accidental low-resistance connection between two points in a circuit, often causing excess current to flow is a short circuit.

In a short circuit, the current bypasses part of the normal circuit and takes the shortest route.

If a power line goes down, the electricity goes off in the entire area served by that power line. Without a complete circuit, electricity can’t flow. However, if the electricity can find another path, such as through a person’s body to the ground, then it will take that path.

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Electrical Safety – Burns! 45


Warning: GRAPHIC

IMAGE will appear

when clicked (so

don’t look if you

don’t want to see

how electricity can

burn your skin.)

Potential danger

To get an idea of how dangerous a current flowing

through your body may be, consider two important

aspects of electricity:

voltage and amperage.

High voltage is more dangerous than low voltage;

Example: 50 000 V are more likely to kill than 10 V.

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2. When assessing the potential danger of an electrical shock,

which is more important: the voltage or the number of amps?

The number of amps is much more important than

voltage when assessing the potential danger of an

electrical shock:

Voltage jolts but amperage kills.

3. What would you feel if various

currents passed through your body at…

If 0.001 A passed through your body, you would likely not feel it.

Current in the range of 0.015 A to 0.020 A will cause a painful shock, and loss of muscle control. This means a person grabbing a wire at this current level may not be able to let go.

Too much electricity flowing through the body can have extremely harmful effects, including burns and damage to the heart. Current as low as 0.1 A can be fatal.

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4. A downed power line is touching a truck.

Why should the driver stay in the truck?

The power line is touching the ground. If he steps to the ground, he would provide a path for the electricity to flow through him to the ground, thus creating a short circuit.

Note: if he must leave, he should jump free, not step out.

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5. How do insulators affect current flow?

List 3 examples of good insulators.

Current does not flow easily through insulators such as wood, rubber, and air.

An insulator strongly resists the flow of electricity.

Other substances such as mud and damp soil conduct electricity somewhat.

Thus, you might feel just a tingle if you touch an electrified fence on a dry day when you are wearing running shoes. But you could get a nasty shock if you touch the fence when you are barefoot in the rain.

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6. What must every plug-in device sold in

Canada list on its label?

Every plug-in device sold in Canada must have a label listing what voltage it requires and the maximum current it uses.

Usually, this label is on the back or bottom of the appliance.

The higher the voltage or current, the more harm the device can do if it malfunctions.

Apple iPhone Voltage and Amperage


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7. Electrical Safety Pointers

Pg. 285

8. Compare and contrast fuses and

circuit breakers.

Fuses and circuit breakers interrupt a circuit when

too much current is flowing through it.

Fuses contain a thin piece of metal that is specially

designed to melt if too much current passes through

it.

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8. Compare and contrast fuses and

circuit breakers.

Most household circuit breakers also have a special wire that heats up if there is too much current.

Instead of melting, the hot wire triggers a spring mechanism that turns off the switch inside the circuit breaker. As soon as the wire has cooled, the circuit breaker can be turned back on.

9. Where is lightning most likely

to hit?

Lightning is a huge amount of negative charge and tends to seek the highest point on the horizon to discharge.

Therefore, avoid standing on hilltops or under trees, or holding objects over your head (especially metal ones) if you are out in a thunderstorm.

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9. How are tall buildings protected

from lightning strikes?

Because tall buildings are a natural target for strikes, lightning rods are often added to their peaks.

Lightning rods are connected to the ground with a wire. Instead of the lightning destroying the building’s roof or electrical wiring, the discharge is conducted harmlessly to the ground.

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Struck By Lightning


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10. What is meant by a “ground wire”?

The grounded three-prong has an extra wire that

connects the device to the ground wire of the

building.

As you can tell by its name, the ground wire leads

to the ground. It provides another pathway for

electricity, just in case there is a short circuit in the

device. It’s better to have electricity travel to the

ground than through an unfortunate user!

Ground Wire

11. You notice a friend removing the third prong of a plug so

that the plug will fit into an extension cord that has only two

holes. Is the removal of this third prong safe? Explain.


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Removing the third prong is a bad idea. This prong

connects the device to the ground, providing a route

for dangerous current to flow in the event of a short

circuit in the device. If the prong is removed, it is

more likely a short circuit could result in someone

being electrocuted.

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Homework!

Read Textbook

Pages 288 – 294

Key Terms

Topic 1.4

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1.4 Cells and Batteries


and stored.

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1. What is an electrochemical cell?

An electrochemical cell is a package of chemicals

designed to produce small amounts of electricity.

The electricity the cell produces comes from chemical

reactions and supplies a steady current.

Example:

Pacemaker

2. What is a dry cell? Give an example of

a device that uses a dry cell.

A cell that has its electrolyte in the form of a paste,

usually in a sealed case, is a dry cell.

This is the type of cell commonly used in portable

devices such as flashlights and portable radios

An electrolyte is a paste or liquid that conducts

electricity because it contains chemicals that form

ions.

http://en.wikipedia.org/wiki/Image:Pacemaker_GuidantMeridianSR.jpg

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3. What is an electrolyte?

An electrolyte is a paste or liquid that conducts

electricity because it contains chemicals that form

ions.

Recall: An ion is an atom or a group of atoms that

has become electrically charged through the loss or

gain of electrons from one atom to another.

3. What is an electrolyte? What does it

react with?

The electrolyte reacts with the two metals, called electrodes. Conductor through which

electric current enters or leaves a device or material

As a result of this reaction, one electrode becomes positively charged, and the other becomes negatively charged.

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4. Why are alkaline cells the most

common type of dry cell?


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Alkaline cells have become the most common type

of dry cell because they offer a good combination

of:

Cost

Electricity output

Shelf life

Reliability

Leak resistance

Dry Cell (Battery)

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5. In the electrochemical cell to the right, label the

positive electrode, negative electrode, and electrolyte.


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electrolyte

positive electrode

(+) cathode negative electrode

(−) anode

electrolyte

salt bridge

e−

6. Describe the components of a wet cell and explain how the

cell produces electricity. Give an example of a device that uses

a wet cell.

A wet cell is an electrochemical cell having a liquid

electrolyte.

They are wet; a wet cell uses a liquid electrolyte

that is usually an acid, such as sulphuric acid.

Example: a car battery

Wet cells are generally cheaper and easier to make

than dry cells. However, care must be taken not to spill

the liquid electrolyte, which may be highly corrosive.

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a wet cell.



a wet cell.


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7. What is the difference between a

primary cell and a secondary cell?

Primary cells produce

electricity from

chemical reactions that

cannot be reversed

Example: A non-

rechargeable battery.

A rechargeable cell

The chemical reactions can be reversed by using an external electrical source to run electricity back through the cell.

The reversed flow of electrons restores the reactants that are used up when the cell produces electricity.

Example: Laptops, cell phones

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Primary Cell Secondary Cell

8. What is the difference between a

cell and a battery?

One electrochemical

cell

A set of 2 or more

cells connected

together

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Cell Battery

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Humphry Davy connected 2000 cells together to form one battery.

Many cells = more voltage and power

Figure 1.25 – pg. 292

9. What is electrochemistry?

Davy’s battery was so powerful that he was able to

separate pure metals out of molten compounds and

ores. Using electrolysis, Davy discovered potassium,

sodium, and other elements.

The work of Davy and others led to a whole new field

of science: electrochemistry. Obtaining electricity from

a chemical cell and electrolysis are just two of the many

applications of electrochemistry.

Electrochemistry is the study of chemical reactions

involving electricity.

http://en.wikipedia.org/wiki/Image:Sir_Humphry_Davy2.jpg

http://en.wikipedia.org/wiki/Image:Faraday-Daniell.PNG

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10. What is electrolysis? Give an example of

how it may be used in real life.

Electrolysis is the decomposition of a substance by an electric current Splits a water molecule into hydrogen gas and oxygen gas, providing a source of fuel.

Recall:

lysis = break down

electro = electricity




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Example:

chlorine produced by electrolysis is used to make drinking water safe.

produce polyvinyl chloride (PVC) products such as pipe and wire insulation.

Electrolysis of water produces the fuel for the space shuttle, pure hydrogen and oxygen. When these two gases are mixed and ignited, they release a tremendous amount of energy, making these two elements a powerful rocket fuel.

11. Describe the process of electroplating.

Use of electricity to coat a thin layer of metal onto an object.

The item to be coated and a bar of the coating metal are immersed in an electrolyte, like the electrodes in a wet cell. A source of electricity is connected between the two metals. The flow of electricity through the electrolyte deposits atoms from the positively charged metal onto the negatively charged one.

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12. A car designer has proposed a new car battery. She is planning to test

different combinations of zinc and carbon electrodes (i.e. both zinc, both

carbon, or zinc and carbon). Will all of these combinations work? Explain

why or why not?


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In order to get a potential difference (voltage), we

need different metals.

Both zinc electrodes – won’t work

Both carbon electrodes – won’t work

Zinc and carbon – will work

Homework!

Review Section 1.0

Textbook

Notes

Section 1.0 Review

Handout

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