Learning with PurposeSlide 1

Learning with PurposeSlide 1

Chapter 1: Quantities and Units

Instructor: Jean-François MILLITHALER

http://faculty.uml.edu/JeanFrancois_Millithaler/FunElec/Spring2017

Learning with PurposeSlide 2

10x

Power of Ten

Base Exponent

104 = 1 x 104 = 10000 = 10,000

0.00000000000000000016 = 1.6 x 10-19

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Convenient method for expressing large and small numbers

Examples:

23,000,000 = 2.3 x 107 (Scientific Notation)= 23 x 106 (Engineering Notation)

0.0000000055 = 5.5 x 10-9 (Scientific Notation)= 55 x 10-10 (Engineering Notation)

Use EE Key on your calculator

Scientific and Engineering Notation

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Interesting point: Water

1x10-3 L (1 mL) = 1 cm-3 = 1 g

Requires 1 cal of energy to heat up of 1 K

Corresponds to 1% between freezing and boiling point

International System SI

Quantity Unit Symbol

Length Meter m

Mass Kilogram kg

Time Second s

Electric current Ampere A

Temperature Kelvin K

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Metric and Imperial Systems

Examples

FAHRENHEIT CELCIUS KELVIN

212 100 373.15 Water boils

98.6 37 310 Human body temperature

68 20 300 Room temperature

32 0 273.15 Water freezing

-320 -195 77 Liquide Nitrogen temperature

-459.67 -273.15 0 Absolute zero

Learning with PurposeSlide 6

Units are based on fundamental units from the MKS system

Meter-Kilogram-Second

Important Electrical Units

Quantity Unit Symbol

Current Ampere A

Charge Coulomb C

Voltage Volt V

Resistance Ohm W

Power Watt Watt

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P

T

G

M

k

Engineering Metric Prefixes

m

m

n

p

f

Peta

Tera

Giga

Mega

kilo

milli

micro

nano

pico

femto

1015

1013

109

106

103

10-3

10-6

10-9

10-12

10-15

Learning with PurposeSlide 8

Convert 0.03 MV to kilovolts (kV)

• 0.03 MV = 0.03 x 106 V = 3 x 10-2 x 103 x 103 V = 30 kV

Convert 470,000 pA to milliamperes (mA).

• 4.7 x 105 x 10-12 A = 4.7 x 10-4 x 10-3 A = 4.7 x 10-4 mA

Add 0.06 MW and 95 kW and express the result in kW.

• 6 x 10-2 x 106 + 95 x 103 = 6 x 104 + 9.5 x 104 = 15.5 x 104 W

• = 155 kW = 0.155 MW

Add 50 mV and 25,000 mV and express the result in mV.

• 50 x 10-3 + 25 x 103 x 10-6 = (50 + 25) x10-3 V = 75 mV

Metric Conversion

Examples

kV3 x 10-2+3

Learning with PurposeSlide 9

Error is the difference between the true or best accepted value and the measured value

Accuracy is an indication of the range of error in a measurement

Precision is a measure of repeatability

Error, Accuracy, and Precision

Physicist Tv

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When reporting a measured value, one uncertain digit may be retained but other uncertain digits should be discarded. Normally this is the same number of digits as in the original measurement.

Example

• 1.0 divided by 3.0 = 0.333333

• 1.0 and 3.0 have 2 significant digits

• Result with same uncertainty = 0.3

Significant Digits

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Rules for determining if a reported digit is significant are: • Nonzero digits are always considered to be significant.

• Ex: 543.26

• Zeros to the left of the first nonzero digit are never significant.

• Ex: 0.000548

• Zeros between nonzero digits are always significant.

• Ex: 6904.903

• Zeros to the right of the decimal point for a decimal number are significant.

• Ex: 8.00

• Zeros to the left of the decimal point with a whole number may or may not be significant depending on the measurement.

• Ex: 4000 does not have a clear number of significant digits

Significant Digits

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Rounding is the process of discarding meaningless digits. Rules for rounding are:

• If the digit dropped is greater than 5, increase the last retained digit by 1

• If the digit dropped is less than 5, do not change the last retained digit.

• If the digit dropped is 5, increase the last retained digit if it makes it even, otherwise do not. This is called the "round-to-even" rule.

Rounding numbers

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Outlet: 120 V in USA, 220 V in Europe

Circuits protected with Ground-Fault Circuit Interrupter (GFCI)

Utility voltages

Safety

Neutral Hot

Ground

Reset

Test

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Safety is always a concern with electrical circuits. Knowing the rules and maintaining a safe environment is everyone’s job.

A few important safety suggestions are:

• Do not work alone, or when you are drowsy.

• Do not wear conductive jewelry.

• Know the potential hazards of the equipment you are working on; check equipment and power cords frequently.

• Avoid all contact with energized circuits; even low voltage circuits.

• Maintain a clean workspace.

• Know the location of power shutoff and fire extinguishers.

• Don’t have food or drinks in the laboratory or work area.

Electrical Safety