ELECTRICITY & MAGNETISM (Fall 2011) LECTURE # 1 BY MOEEN GHIYAS.

ELECTRICITY & MAGNETISM (Fall 2011)

LECTURE # 1

BY

MOEEN GHIYAS

TODAY’S LESSON

ENGINEERING DEFINITIONS &

CHAPTER 1 – Introductory Circuit Analysis by Boylested

Today’s Lesson Contents

• A Brief History & Definitions

• Units of Measurement & System of Units

• Conversion Within and Between System of Units

• Problem # 38 Solving – Ch 1

• Significant Figures, Accuracy and Rounding off

• Fixed-point, Floating-point, Scientific & Engineering

Notation and Prefixes

• Powers of Ten

• Conversion Between Levels of Powers of Ten

A Brief History of Electrical Engg

• The spectacle of lightening is as old as the age of earth

and the phenomenon of static electricity has been toyed

with since antiquity (400 BC – Frog eg).

• The Greeks so often used to demonstrate the effects of

static electricity elektron, but no extensive study was

made of the subject until 1600s.

• In the early stages, the contributors were not engineers

but instead physicists, chemists, mathematicians, or

even philosophers.


• However, the first electrical engineer is considered to be

William Gilbert (a physicist), with his 1600 publication of De

Magnete, who was the originator of the term "electricity“.

• In later years, Otto von Guericke, developed the first

machine to generate large amounts of charge, and

Stephen Gray, was able to transmit electrical charge

over long distances on silk threads.

• Charles DuFay demonstrated that charges either attract

or repel each other, leading him to believe that there

were two types of charges (+ve and –ve charges).


• In 1784, Charles Coulomb demonstrated in Paris that

the force between charges is inversely related to the

square of the distance between the charges.

• Hans Christian Oersted, a Swedish professor of

physics, announced in 1820 a relationship between

magnetism and electricity that serves as the foundation

for the theory of electromagnetism as we know it today.


• In the same year 1820, a French physicist, André

Ampère, demonstrated that there are magnetic effects

around every current-carrying conductor and that

current-carrying conductors can attract and repel each

other just like magnets.

• In 1831, an English physicist, Michael Faraday,

demonstrated his theory of electromagnetic induction,

whereby a changing current in one coil can induce a

changing current in another coil, even though the two

coils are not directly connected.


• Professor Faraday also did extensive work on a

storage device he called the condenser, which we

refer to today as a capacitor.

• The first voltaic cell, with its ability to produce

electricity through the chemical action of a metal

dissolving in an acid, was developed by another

Italian, Alessandro Volta, in 1799.


• Thus in modern era, electrical engineering can trace

its origins in the experiments of André Ampère and

Alessandro Volta in the 1800s, the experiments of

Michael Faraday, Georg Ohm and others and the

invention of the electric motor in 1872.

• The work of James Maxwell and Heinrich Hertz in the

late 19th century gave rise to the field of Electronics.


• The later inventions of the vacuum tube and the

transistor further accelerated the development of

electronics to such an extent that electrical and

electronics engineers currently outnumber their

colleagues of any other Engineering specialty.

• Note that many of the units of measurement bear the

name of major contributors in those areas — e.g.

– Volt after Count Alessandro Volta, (Italian Physicist)

– Ampereafter André Ampère, (Italian Physicist)

– Ohm after Georg Ohm. (German Physicist)

Definitions

• Who is an Engineer?

– An engineer is one who analysis complex

problems of world, solves the problems by

simplification methods and presents a practical

solution.

Definitions

• Electricity (from the New Latin ēlectricus,

meaning "amber-like") is a general term that

encompasses a variety of phenomena

resulting from the presence and flow of

electric charge.

• Electrostatics deals with static electricity i.e

static electric charges and field exerted by the

them in their surroundings.

Definitions

• Electrostatics & Electricity in more precise

terms

– Electric charge – a property of some subatomic

particles, which determines their electromagnetic

interactions. Electrically charged matter is

influenced by, and produces, electromagnetic fields.

– Electric current – a movement or flow of

electrically charged particles, typically measured in

amperes.

Definitions

– Electric field – an influence produced by an electric

charge on other charges in its vicinity.

– Electric potential – the capacity of an electric field

to do work on an electric charge, typically measured

in volts.

– Electromagnetism – a fundamental interaction

between the magnetic field and the presence and

motion of an electric charge.

System of Units

• The International Bureau of Weights and Measures

located at Sèvres, France, has been the host for the

General Conference of Weights and Measures,

attended by representatives from all nations of the

world.

• In 1960, the General Conference adopted a system

called Le Système International d’Unités (International

System of Units), which has the international

abbreviation SI.

System of Units

• SI has been adopted by the Institute of

Electrical and Electronic Engineers, Inc. (IEEE)

in 1965 and by the United States of America

Standards Institute in 1967 as a standard for all

scientific and engineering literature.

System of Units

System of Units - Comparison

The The meter was originally defined meter was originally defined in 1790 to be 1/10,000,000 in 1790 to be 1/10,000,000

the the distance between the equator and either pole at sea level, a distance between the equator and either pole at sea level, a

length preserved on a platinum-iridium bar at the International length preserved on a platinum-iridium bar at the International

Bureau of Weights and Measures at Sèvres, France.Bureau of Weights and Measures at Sèvres, France.

The The meter is now defined meter is now defined with reference to the speed of with reference to the speed of

light in a vacuum, which is 299,792,458 m/s.light in a vacuum, which is 299,792,458 m/s.


The The kilogram is defined kilogram is defined as a mass equal to 1000 times the as a mass equal to 1000 times the

mass of one cubic centimeter of pure water at 4°C.mass of one cubic centimeter of pure water at 4°C.


• The The secondsecond was was originally defined originally defined as 1/86,400 of as 1/86,400 of

the mean solar the mean solar day. However, since Earth’s rotation day. However, since Earth’s rotation

is slowing down by almost 1 second every 10 years,is slowing down by almost 1 second every 10 years,

• the second was the second was redefined in 1967 redefined in 1967 as 9,192,631,770 as 9,192,631,770

periods of the electromagnetic radiation emitted periods of the electromagnetic radiation emitted

by a particular transition of cesium atom.by a particular transition of cesium atom.

Units of Measurement

• Students often generate a numerical solution but often

they are unsure of which unit of measurement should

be applied. Consider, for example

d = 4000 ft

t = 1 min

V =? mi /hr

Units of Measurement

• To state that v = 45.37 without including the unit of

measurement mi/h is meaningless.

• Note while working with an equation, each quantity is in

the same system of units

Conversion Within and Between System of Units

• This operation is performed incorrectly most often

• Just convert the conversion factor into ratio or fraction

with required system of units in numerator and the other

in denominator.

• For conversion factor of 1m = 39.37 in

• To convert inches to meter (1m/39.37in) or

• To convert meter to inches (39.37in/1m)

Conversion Within and Between System of Units

• Let us convert 48 in. (4 ft) to meters

– We know conversion factor, 1 m = 39.37 in.

• Dividing both sides of the conversion factor by 39.37 in.

will result in the following format:

• Substituting we have,

Problems – Ch 1

• # 38 - Each spring there is a race up 86 floors of the 102-

story Empire State Building in New York City. If you were able to

climb 2 steps/second, how long would it take you to reach the

86th floor if each floor is 14 ft. high and each step is about 9 in.?

• Solution

– Steps – Find no of steps (distance) up to 86th floor and then time taken to

cover that

distance

Significant Figures

• All nonzero numbers are considered significant

figures, with zeros being significant in only some

cases.

• For instance, the zeros in 1005 are considered

significant because they define the size of the number

and are surrounded by nonzero digits.

• For the number 0.4020, the zero to the left of the

decimal point is not significant, but the other two are

because they define the magnitude and the fourth-

place accuracy of the reading.

Accuracy (or Precision in Measurement)

• Measurements of 22.1 and 22.10 imply different levels

of accuracy. The first suggests that the measurement

was made by an instrument accurate only to the tenths

place; the latter was obtained with instrumentation

capable of reading to the hundredths place.

• In the addition or subtraction of approximate numbers,

the entry with the lowest level of accuracy determines

the format of the solution. For example,

532.6 + 4.02 + 0.036 = 536.656 ≈ 536.7

(as determined by 532.6)

Accuracy (or Precision in Measurement)

• For the multiplication and division of approximate

numbers, the result has the same number of significant

figures as the number with the least number of

significant figures.

0.0046/0.05 = 0.0920 ≈ 0.09 (as determined by the one

significant digit of 0.05)

Rounding off

• For approximate numbers (and exact, for that matter)

there is often a need to round off the result; that is, you

must decide on the appropriate level of accuracy.

• The accepted procedure is simply to note the digit

following the last to appear in the rounded-off form, and

add a 1 to the last digit if it is greater than or equal to 5,

and leave it alone if it is less than 5.

• For example, 3.186 ≈ 3.19 ≈ 3.2, depending on the

level of precision desired.

Fixed-point, Floating-point, Scientific & Engg Notation

• There are four ways in which numbers appear when

using a computer or calculator

• Fixed-point – The fixed-point format defines the no. of

digits appearing after decimal point each time.

• Floating-point – In the floating-point format, the no. of

digits appearing after the decimal point are defined by

the number to be displayed.


• Scientific (also called standard) notation and

engineering notation make use of powers of ten.

• Scientific notation requires that the decimal point

appear directly after the first digit greater than or equal

to 1 but less than 10.

• A power of ten (notation E or x10y ) will then appear

with the number, even if it has to be to the zero power.


• Within the scientific notation, the fixed- or floating-point

format can be chosen.

• Floating Point Scientific

• If Fixed Point Scientific is chosen and set at the

thousandths-point accuracy, we have


• Engineering Notation – Specifies that all powers of ten

must be multiples of 3, and the mantissa must be

greater than or equal to 1 but less than 1000.

• This restriction on the powers of ten is due to the fact

that specific powers of ten have been assigned

prefixes e.g. Kilo, micro etc

• Engineering notation with three-place accuracy (fixed

point notation) will result in

Powers of Ten• An important mathematical equation pertaining to

powers of ten is:

• Shifting a power of ten from the denominator to the

numerator, or the reverse, requires simply changing

the sign of the power.

• 1 = 100 1/10 = 0.1 = 10-1

• 10 = 101 1/100 = 0.01 = 10-2

• 100 = 102 1/1000 = 0.001 = 10-3

• 1000 = 103 1/10,000 = 0.0001 = 10-4

Powers of Ten

• The product of powers of ten:

• The division of powers of ten:

• The power of powers of ten:

• Multiplication,

Powers of Tens

Prefixes of SI Units

Conversion Between Levels of Powers of Ten

• An increase or a decrease in the power of ten must be

associated with the opposite effect on the multiplying

factor. For example

– Convert 20 kHz to megahertz.

Conversion Between Levels of Powers of Ten

• An increase or a decrease in the power of ten must be

associated with the opposite effect on the multiplying

factor. For example

– Convert 0.01 ms to microseconds.

Powers of Ten (Example)

• Example 1.1 - Determine appropriate prefixes

• Last part solution is it correct in engineering notation?

Summary / Conclusion

• A Brief History & Definitions

• Units of Measurement & System of Units

• Conversion Within and Between System of Units

• Problem # 38 Solving – Ch 1

• Significant Figures, Accuracy and Rounding off

• Fixed-point, Floating-point, Scientific & Engineering

Notation and Prefixes

• Powers of Ten

• Conversion Between Levels of Powers of Ten

ELECTRICITY & MAGNETISM (Fall 2011) LECTURE # 1 BY MOEEN GHIYAS.

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Transcript of ELECTRICITY & MAGNETISM (Fall 2011) LECTURE # 1 BY MOEEN GHIYAS.