NS2 5.3 Basic Electricity

CHAPTER 3

BASIC ELECTRICITY

The study of

electricity began

with the ancient

Greeks.

Rubbing amber with a cloth created a

force that attracted the cloth to the

amber.

Rubbing two pieces of amber with two

cloths caused the cloths to repel one

another as much as they were attracted

to the amber.

The forces the Greeks observed were

called electric (from the Greek word for

amber).

The cloths and amber were said to be

electrically charged.

The Greeks could

not explain electrical

force.

The true cause of electricity wasdetermined with the developmentof the atomic theory of matter.

The presence and motion of

electrons, protons, and other

charged particles

Manifests itself as attraction,

repulsion, luminous and heating

effects

Electricity

Scientists could explain electricalcharges when they found atoms werecomposed of negatively chargedparticles (electrons) orbiting positivelycharged particles (protons) andneutrons which have no charge.

Under most conditions, an atom will

have no charge.

If the number of electrons is increased,

an atom becomes negatively charged.

If electrons are removed, an atom will

have a positive charge.

Charged atoms are called ions.

Unlike charges

attract each other

while like charges

repel each other.

In the atom, electrons are held in their

orbit by the attractive force between

them and protons in the nucleus.

In the Greeks' experiments with amber,

the cloth picked up electrons from the

amber, becoming negatively charged.

This left the amber with a positive

charge, and unlike charges attract

one another.

Conductors and Insulators

ConductorInsulator

An electric charge can move through

a material if it has a large number of

free electrons.

Electrons can easily move from atom

to atom in material with a large number

of free electrons.

Substances that allow free movement of

electrons due to their atomic structure

are called conductors.

A material or object that permits an

electric current to flow easily

Conductor

Silver, copper, and aluminum wire, in

that order, are the best conductors.

Copper and aluminum wire are the most

commonly used because they are the

the least expensive.

Electrical energy is conveyed as a wave

traveling at the speed of light through

conductors by free electrons.

As the electrical energy passes, each

electron moves a short distance to the

next atom, displacing one or more

electrons by forcing them out of their

orbits.

The replaced electrons repeat the

process in other nearby atoms.

Some substances have very few

free electrons and are therefore

poor conductors.

Wood

Rubber

Glass

These substances, such as rubber,

glass, or dry wood, are called insulators.

Materials that are poor conductors

(as in electricity or heat)

Materials that have few free electrons

Insulators

Good conductors such as wire carry

electricity and are covered by insulating

material to prevent electricity from being

diverted from the conductors.

ConductorInsulator

Voltage

The force that causes electricity to

move in a conductor is called voltage (V)

or electromagnetic force (E).

Electric potential or potential

difference expressed in volts

Voltage

Something that moves or tends to

move electricity; the potential

difference derived from an electrical

source per unit quantity of electricity

passing through the source (such as

a cell or generator)

Electromotive Force

Six Basic Ways to Generate Voltage

• Friction

• Pressure

• Heat

• Light

• Chemical action

• Magnetism

Friction

Voltage can be produced by rubbing

two materials together.

Static electricity is the most common

name for electricity generated through

friction.

Static electricity occurs frequently in

dry climates or during low humidity.

Pressure

Voltage can be produced by squeezing

crystals such as natural quartz or

manufactured crystals.

Compressed electrons tend to move

through a crystal at predictable

frequencies.

Crystals are frequently used in

communications equipment.

Heat

Voltage can be produced by heating the

place where two unlike metals are joined.

The hot junction where the moving

electrons from the metals meet is

called a thermocouple.

A device for measuring temperature

in which a pair of wires of dissimilar

metals (such as copper and iron) are

joined and the free ends of the wires

are connected to an instrument (such

as a voltmeter) that measures the

difference in potential created at the

junction of the two metals

Thermocouple

The difference in temperature of the two

metals determines the amount of voltage.

Thermocouples are often used to

measure and regulate temperature,

as in a thermostat.

Light

Voltage can be produced when light

strikes a photosensitive (light-sensitive)

substance.

Light dislodges electrons from their

orbits around surface atoms.

Voltage produced in this manner is called

photoelectric.

Involving, relating to, or utilizing any

of various electrical effects due to

the interaction of radiation (such as

light) with matter

Photoelectric

The photoelectric cell is the device

that operates on this principle.

A plate coated with compounds ofsilver or copper oxide, which areextremely sensitive to light, can alsoproduce a flow of electrons.

Light is used to generate voltage indevices requiring extreme precision such as television cameras andburglar alarms.

Chemical Action

Voltage can be produced by chemical

reactions, as in a battery cell.

A simple voltaic battery consists of a

carbon strip (positive) and a zinc strip

(negative) suspended in a solution of

water and sulfuric acid.

The solution is called the electrolyte.

The chemical action that results from

this combination causes electrons to

flow between the zinc and carbon

electrodes.

Equipment

AircraftAutomobile

Boats

Batteries are used as sources of

electrical energy in automobiles, boats,

aircraft, ships, and portable equipment.

Magnetism

Voltage can be produced when a

conductor moves through a magnetic

field cutting the field's line of force.

This method is used in electrical

generators and is the most common

source of power.

Usually, a copper-wire conductor

is moved back and forth through

the magnetic field created by a

U- or C-shaped electromagnet.

Voltmeter

An instrument designed to measure

voltage in an electrical circuit is called

a voltmeter.

The movement of electrons

through a conductor

Electrical Current

A flow of electric charge;

also, the rate of such flow

Current

Direct

Current

Alternating

Current

There are two general types of electrical

current: direct and alternating currents.

Direct current flows continuously

in the same direction.

Alternating current periodically

reverses direction.

An ampere (or amp) is the unit used

to measure the rate of current flow.

The symbol for current flow is I.

Ammeter

An instrument designed to measure

electrical current is called an ammeter.

Every material offers some resistance

or opposition to electric current flow.

Good conductor

Very little resistance

Insulator/poor conductor

High resistance

The size and composition of wires in

an electric circuit are designed to

keep resistance as low as possible.

A wire's resistance depends on:

• Length

• Diameter

• Composition

• Temperature

Manufactured circuit elements that

provide a measured amount of

resistance are called resistors.

Resistance is measured in ohms

(symbol: Ω, the Greek letter omega).

The resistance of a circuit element

(or circuit) that permits a steady

current of one ampere to flow when

a constant potential difference of

one volt is applied to that circuit

Ohm

One ohm is the resistance of a circuit

that permits one ampere to flow when

a potential difference of one volt is

applied to the circuit.

The opposition offered by a body or

substance to the passage through

it of a steady electric current

Resistance

Ohmmeter

An instrument used to measure

resistance in an electrical circuit

is called an ohmmeter.

Batteries

A battery consists of one or more cells

assembled in a common container to

act as a source of electrical power.

A cell is the fundamental

unit of a battery.

A simple cell consists of two electrodes

placed in a container of electrolyte.

Electrodes

Conductors by

which current

leaves or returns

to the electrolyte

Electrodes

Carbon Zinc

In a simple cell, electrodes are carbon

and zinc strips placed in

electrolyte.

Zinc Container

Carbon Rod

Ammonium

Chloride

Paste

In a dry cell battery,

there is a carbon rod

in the center of an

ammonium chloride

paste, which is encased

in a zinc container.

The electrolyte may be a salt, acid,

or an alkaline solution.

In an automobile battery, the

electrolyte is in liquid form.

In a dry cell battery,

the electrolyte is a

paste.

ZincCopper

A primary cell is one in which the

chemical action eats away one of

the electrodes.

Eventually the electrode must be

replaced or the cell discarded.

In the case of a common dry cell

(flashlight battery), it is usually

cheaper to buy a new cell.

A secondary cell is one in which the

electrodes and electrolyte are altered

by a chemical action that generates

current.

These cells can be recharged by

forcing an electric current through

them in a direction opposite to

the current discharge.

A common example of a

secondary cell battery is

the automotive battery.

The Electrical Circuit

A pathway for electrons and current flow

is created when two unequal charges are

connected by a conductor.

Voltage

Source

Conductor

An electric circuit is a conducting

pathway consisting of the conductor

and a path through the voltage source.

A lamp connected by wires to a dry cell's

terminals forms a simple electric circuit.

The electron current flows from the

negative (-) terminal of the battery

through the lamp to the positive (+)

battery terminal.

The electron current continues by

going through the battery from the

(+) terminal to the (-) terminal.

Closed

Current will flow as long as the circuit

remains closed.

The Electron

Before electrons were discovered, it was

wrongly assumed that current was a

flow of positive charges from positive

to negative terminals in a circuit.

A diagram in which symbols are

used for a circuit’s components,

instead of pictures

A structural or procedural diagram,

especially of an electrical or

mechanical system

Schematic

Transformer

Switch (open)

Switch (closed)

Symbols are used to make diagrams

easier to draw and understand.

Schematic diagrams aid technicians

who design or repair electrical and

electronic equipment.

Ohm's Law

George Ohm

Proved a definite

relationship exists

among current,

voltage, and

resistance

Ohm's Law

The current in a circuit is directly

proportional to the applied voltage

and inversely proportional to the

circuit resistance.

Ohm's Law

I = current in amperes

E = voltage in volts

R = resistance in ohms

If any two of the quantities

In the equation are known,

The third may be easily found.

R

EI

VOLTAGE

The unit used to measure the rate

at which current flows

Ampere

I =ER

Equation A

(The formula for finding current)

E1.5 v

R1.5 Ω

Circuit 1

Determining current in a basic circuit

I = ?

E1.5 v

R1.5 Ω

Circuit 1

Circuit 1 contains a resistance of 1.5

ohms and a source

voltage of 1.5 volts.

I = ?

How much current

flows in the circuit?

E1.5 v

R1.5 Ω

Circuit 1

I = 1 ampere

SOLUTION

I =ER

I =1.51.5

In many circuit applications, the current

is known, and either the voltage or

resistance will be the unknown quantity.

Equation B

E = IR

(The formula for finding voltage)

E= ?

R1.5 Ω

I = 1a

Find the voltage in this basic circuit.

E= ?

R1.5 Ω

I = 1a

Find the voltage in this basic circuit.

E =1_

1.5

E = 1.5V

Equation C

(The formula for finding resistance)

R =EI

E1.5v

R= ? Ω

I = 1a

Find the resistance in this basic

circuit.

R =E I

E1.5v

R= ? Ω

I = 1a

Find the resistance in this basic

circuit.

R =1.5 1

R = 1.5

Power

Electrical Power (P)

The rate at which work is being

done (voltage making current flow)

Work is done

whenever a force

causes motion.

Since voltage makes current flow in a

closed circuit, work is being done.

Electric power rate

is measured by the

watt - the basic unit

of power.

Power is equal to the voltage across

a circuit, multiplied by the current

through the circuit.

P = IE

Using P as the symbol for electrical

power, the basic power formula is:

4P = 2E2I

As an example, when E equals 2 volts

and I equals 2 amperes, P equals

4 watts.

E

200 volts

R2

30 Ω

I = 2 amps

R1

20 Ω

R3

50 Ω

E

400 volts

R2

30 Ω

I = 4 amps

R1

20 Ω

R3

50 Ω

In drawing 1, the total voltage is 200 volts. In drawing 2, the amps were doubled, 2 to 4, thusresulting in the voltage being 400 volts. When voltage is doubled and resistance remains unchanged, power is doubled twice.

Drawing 1 Drawing 2

Doubling voltage causes a doubling of

current that doubles both of the factors

that determine power.

The rate of change of power, in a

circuit of fixed resistance, is the

square of the change in voltage.

The basic power formula (P = IE)

may also be expressed as:

P = E²/R

or

P = I²R

Q.1. Who began the study of

electricity?

A.1. Ancient Greeks

Q.1. Who began the study of

electricity?

Q.2. What is an ion?

A.2. A charged atom

Q.2. What is an ion?

Q.3. What is the force that causes

electricity to move through a

conductor called, and what is its

symbol?

A.3. Voltage; E

Q.3. What is the force that causes

electricity to move through a

conductor called, and what is its

symbol?

Q.4. What is the most common name

for the voltage produced by

rubbing two materials together?

A.4. Static electricity

Q.4. What is the most common name

for the voltage produced by

rubbing two materials together?

Q.5. Why is the voltage produced by

squeezing crystals useful in

communications equipment?

A.5. Because the voltage produced

will be at predictable

frequencies

Q.5. Why is the voltage produced by

squeezing crystals useful in

communications equipment?

Q.6. Why are thermocouples often

used to measure or regulate

temperature?

A.6. Because the difference in the

temperature of the metals

determines the voltage

Q.6. Why are thermocouples often

used to measure or regulate

temperature?

Q.7. What is the voltage called that

is produced when light strikes a

photosensitive (light sensitive)

substance?

A.7. Photoelectric voltage

Q.7. What is the voltage called that

is produced when light strikes a

photosensitive (light sensitive)

substance?

Q.8. What is a common source of

electrical energy in automobiles,

boats, and aircraft?

A.8. The secondary (wet) cell battery

Q.8. What is a common source of

electrical energy in automobiles,

boats, and aircraft?

Q.9. What method is used to

produce electric energy in

electric generators?

A.9. Magnetism

Q.9. What method is used to

produce electric energy in

electric generators?

Q.10. What are the two types of

electric current?

A.10. Direct and alternating

Q.10. What are the two types of

electric current?

Q.11. What is the unit called that is

used to measure the rate at

which current flows, and what

is its symbol?

A.11. The Ampere; I

Q.11. What is the unit called that is

used to measure the rate at

which current flows, and what

is its symbol?

Q.12. Wires in an electric circuit are

designed to keep what at a

minimum?

A.12. Electrical resistance

Q.12. Wires in an electric circuit are

designed to keep what at a

minimum?

Q.13. What are circuit elements

called that are manufactured to

provide a definite specified

amount of resistance?

A.13. Resistors

Q.13. What are circuit elements

called that are manufactured to

provide a definite specified

amount of resistance?

Q.14. What is the unit of

measurement of resistance,

and what is its symbol?

A.14. The Ohm; R


measurement of resistance,

and what is its symbol?

Q.15. What is the fundamental unit

of a battery called?

A.15. A cell

Q.15. What is the fundamental unit

of a battery called?

Q.16. What is the cell called in which

carbon and zinc strips are

placed in a container holding

an electrolyte?

A.16. A simple cell


carbon and zinc strips are

placed in a container holding

an electrolyte?


a carbon rod is placed in a zinc

container with an electrolyte

paste?

A.17. A dry cell


a carbon rod is placed in a zinc

container with an electrolyte

paste?

Q.18. What is one of the more

significant features of a battery

composed of secondary cells,

such as an automobile battery?

A.18. It is rechargeable.

Q.18. What is one of the more

significant features of a battery

composed of secondary cells,

such as an automobile battery?

Q.19. What is a conducting pathway

consisting of a conductor and

a path through the voltage

source?

A.19. An electric circuit

Q.19. What is a conducting pathway

consisting of a conductor and

a path through the voltage

source?

Q.20. What is a schematic?

A.20. A diagram in which symbols

are used to represent circuit

components

Q.20. What is a schematic?

Q.21. What is Ohm’s Law?

A.21. I = E/R

(current = volts ÷ resistance)

Q.21. What is Ohm’s Law?

Q.22. Applying Ohm's Law to a

circuit, if source voltage

increases and resistance stays

constant, what will circuit

current do?

A.22. Increase


circuit, if source voltage

increases and resistance stays


current do?


circuit, if resistance increases

and source voltage remains


current do?

A.23. Decrease



and source voltage remains


current do?



and source voltage increases,

what will circuit current do?

A.24. You cannot tell without

knowing actual values.



and source voltage increases,

what will circuit current do?


circuit, if voltage is 10 volts

and resistance is 5 ohms, what

is circuit current?

A.25. I = E/R

I = 10 volts ÷ 5 ohms

I = 2 amps




is circuit current?


circuit, if voltage is 5 volts and

resistance is 2 ohms, what is

circuit current?

A.26. I = E/R


I = 2.5 amps


circuit, if voltage is 5 volts and

resistance is 2 ohms, what is

circuit current?




is circuit current?

A.27. I = E/R


I = 3 amps




is circuit current?


measurement of power?

A.28. The watt


measurement of power?

Q.29. What is the electrical symbol

for power, and what is the

formula for calculating it?

A.29. P; P = IE

(power = amps x volts)

Q.29. What is the electrical symbol

for power, and what is the

formula for calculating it?

Q.30. In a circuit with 200 volts and

20 amps, what is circuit

power?

A.30. P = IE

P = 20 amps x 200 volts

P = 4,000 watts (or 4 kilowatts)



power?



power?

A.31. P = IE


P = 1,000 watts (or 1 kilowatt)



power?


5 amps, what is circuit power?

A.32. P = IE


P = 300 watts


5 amps, what is circuit power?

Q.33. In a circuit with a current of

3 amps and a resistance of 20

ohms, what is circuit power?

A.33. P = I² x R

P = 3² (amps) x 20 ohms

P = 9 x 20

P = 180 watts







A.34. P = I² x R


P = 16 x 25

P = 400 watts







A.35. P = I² x R


P = 25 x 30

P = 750 watts




Education

NS2 5.3 Basic Electricity