ELECTRICALFUNDAMENTALS TOPIC 1Fundamental And Derived Units 1
Learning ObjectivesAt the conclusion of this section, students should beable to: Identify the basic units of measurement Define and use the SI derived units for force, pressure, energy, work, temperature and power Convert units to multiple and sub-multiple units Transpose a given equation for any variable in the equation Perform basic calculations of electrical and related mechanical quantities given any combination of units, multiple units or sub- multiple units. 2
ResourcesHampson & Hanssen, “Electrical Trade Principles – A practical approach” Pgs 2 – 5, 15 – 25 & 421 including review questionsChisholm Moodle E Learning 3
SubstitutionTake the electrical quantities of: Power (P),Voltage (V), Current (I) and Resistance (R). Thereare two equations that use these quantities, theyare: P = V x I and V = I x RSuppose we want to calculate power when onlycurrent (I) and resistance (R) is known.Substitution will enable power to be calculated. 13
Substitution V IRSubstituting IR for V in the power equation, P I R I 2 I R 14
Multiples and Submultiples Pg. 4 Prefix Symbol Exponential Multiplier format tera T 1012 1 000 000 000 000 giga G 109 1 000 000 000 mega M 106 1 000 000 kilo k 103 1 000 milli m 10-3 0.001 micro 10-6 0.000 001 nano n 10-9 0.000 000 001 pico p 10-12 0.000 000 000 001 15
Standard Measurement Units Previous measuring systems Imperial System English units of pound (mass), foot (length) andTo help understand, not for examination degree Fahrenheit (temperature) CGS Units Centimetre for length, gram for mass, second for time MKSA System Metre, (length) Kilogram, (mass) Second (time) and Ampere (electric current) 18
SI (Systeme International)The SI system is an expansion of the MKSAand includes three new base units. These arethe kelvin (temperature), the mol (amount ofMatter} and the candela (luminous intensity).This brought the total number of base units*to seven.*Base units are a set of mutually independent (fundamental)units from which all other units can be derived. 19
Derived Quantities Velocity (distance traveled in a given time) Acceleration (the rate of change in velocity) Force (the physical action capable of moving a body) Torque (twisting force eg produced by a motor) Pressure (force per unit area) Electrical charge (1 Amp flowing for 1 second) Voltage (electrical pressure) Resistance (opposition to current flow) Energy (the capacity to do work) Work (force acting through a distance) Power (rate of doing work) 21
Abbreviations and Conventions(shortened names for things) (agreed standard ways to do or write things)1. There should be a space between the numeric value and the unit symbol. For example five milliamps is written as 5 mA and not 5mA(A ‘hard’ space in a typed document will prevent this; 240 V i.e. the unit symbol appearing on the next line.) 23
Abbreviations and Conventions2. When writing numbers above 999, they should be clustered into groups of three. For example, 1 000 or 20 000 or 0.000 006 78 and not 1000 or 20000 or 0.00000678 (This reduces the chance of mis-reading a number’s size by mis-counting zero’s) 24
Abbreviations and Conventions5. A leading zero should precede a decimal value. For example 0.351 and not .351 (This makes it easier to recognise a missing decimal point, for instance, on a well-used drawing 0 351 would be obvious but 351 could lead to a major error!) 25
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