Chapter 1: Quantities and Units

Transcription

1 Chapter 1: Quantities and Units Instructor: Jean-François MILLITHALER Slide 1

2 Power of Ten Base Exponent 10 x 10 4 = 1 x 10 4 = = 10, = 1.6 x Slide 2

3 Scientific and Engineering Notation Convenient method for expressing large and small numbers Examples: 23,000,000 = 2.3 x 10 7 (Scientific Notation) = 23 x 10 6 (Engineering Notation) = 5.5 x 10-9 (Scientific Notation) = 55 x (Engineering Notation) Use EE Key on your calculator Slide 3

4 International System SI Quantity Unit Symbol Length Meter m Mass Kilogram kg Time Second s Electric current Ampere A Temperature Kelvin K 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 Slide 4

5 Metric and Imperial Systems Examples FAHRENHEIT CELCIUS KELVIN Water boils Human body temperature Room temperature Water freezing Liquide Nitrogen temperature Absolute zero Slide 5

6 Important Electrical Units Quantity Unit Symbol Current Ampere A Charge Coulomb C Voltage Volt V Resistance Ohm W Power Watt Watt Units are based on fundamental units from the MKS system Meter-Kilogram-Second Slide 6

7 Engineering Metric Prefixes P T G M k Peta Tera Giga Mega kilo m m n p f milli micro nano pico femto Slide 7

8 Metric Conversion Examples Convert 0.03 MV to kilovolts (kv) 0.03 MV = 0.03 x 10 6 V = 3 x 10-2 x 10 3 x 10 3 V = 30 kv 3 x kv Convert 470,000 pa to milliamperes (ma). 4.7 x 10 5 x 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 x 10 3 = 6 x x 10 4 = 15.5 x 10 4 W = 155 kw = MW Add 50 mv and 25,000 mv and express the result in mv. 50 x x 10 3 x 10-6 = ( ) x10-3 V = 75 mv Slide 8

9 Error, Accuracy, and Precision 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 Physicist Tv Slide 9

10 Significant Digits 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 = and 3.0 have 2 significant digits Result with same uncertainty = 0.3 Slide 10

11 Significant Digits Rules for determining if a reported digit is significant are: Nonzero digits are always considered to be significant. Ex: Zeros to the left of the first nonzero digit are never significant. Ex: Zeros between nonzero digits are always significant. Ex: 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 Slide 11

12 Rounding numbers 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. Slide 12

13 Utility voltages Safety Outlet: 120 V in USA, 220 V in Europe Neutral Hot Ground Reset Test Circuits protected with Ground-Fault Circuit Interrupter (GFCI) Slide 13

14 Electrical Safety 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. Slide 14