Dies ist eine alte Version des Dokuments!

1. Preparation, Properties, Proportions

1.1 Physical quantities

Learning Objectives

By the end of this section, you will be able to:

  1. know the basic physical quantities and the associated SI units.
  2. know the most important prefixes. You can assign a power of ten to the respective abbreviation (G, M, k, d, c, m, µ, n).
  3. use numerical values ​​and units given in an existing quantity equation. From this you should be able to calculate the correct result with a calculator.
  4. assign the Greek letters.
  5. always calculate with numerical value and unit.
  6. know that a related quantity equation is dimensionless!
The KIT bridging course offers a similar introduction to physical variables

Basic sizes

Brief presentation of the SI units

Base size name unit symbol definition
Time Second s Oscillation of a $ Cä $ atom
Length Meter m about s and the speed of light
Amperage Ampere A via s and elementary charge
Mass Kilograms kg still over kg prototype
Temperature Kelvin K over triple point of water
Amount of substance Mole mol over the number of the $ ^ {12} C $ nuclide
Light intensity Candela cd over specified radiation intensity
Tab. ##: SI units
  • For the practical application of physical laws of nature, physical quantities are put into mathematical relationships.
  • There are basic sizes based on the SI system of units (French for Système International d'Unités), see below
  • In order to determine the basic parameters quantitatively (quantum = Latin „how big“), physical units are defined, e.g. $ meter $ for the length
  • In electrical engineering, the first three basic variables (see Tabelle ##) are particularly important.
    the mass is important for the representation of energy and power.
  • Each physical quantity is indicated by a product of numerical value and unit :
    e.g. $ I = 2 A $
    • This is the short form of $ I = 2 \ cdot 1A $
    • $ I $ is the physical quantity, here: electrical current strength
    • $ \ {I \} = 2 $ is the numerical value
    • $ [I] = 1 A $ is the (measurement) unit, here: ampere

derived quantities, SI units and prefixes

Prefix Prefix characters Meaning
Yotta Y $ 10 ^ {24} $
Zetta Z $ 10 ^ {21} $
Exa E $ 10 ^ {18} $
Peta P $ 10 ^ {15} $
Tera T $ 10 ^ {12} $
Giga G $ 10 ^ {9} $
Mega M $ 10 ^ {6} $
Kilos k $ 10 ^ {3} $
Hecto h $ 10 ^ {2} $
Deka de $ 10 ^ {1} $
Tab. ##: Prefixes I
Prefix Prefix characters Meaning
Deci d $ 10 ^ {- 1} $
Zenti c $ 10 ^ {- 2} $
Milli m $ 10 ^ {- 3} $
Micro u, $ \ mu $ $ 10 ^ {- 6} $
Nano n $ 10 ^ {- 9} $
Pico p $ 10 ^ {- 12} $
Femto f $ 10 ^ {- 15} $
Atto a $ 10 ^ {- 18} $
Zeppto z $ 10 ^ {- 21} $
Yokto y $ 10 ^ {- 24} $
Tab. ##: Prefixes II
  • In addition to the basic sizes, there are also derived sizes, e.g. $ 1 {{m} \ over {s}} $
  • SI units should be preferred for calculations. These can be derived from the basic quantities without a numerical factor .
    • The pressure unit bar ($ bar $) is an SI unit
    • BUT: The outdated pressure unit atmosphere ($ = 1.013 bar $) is not a SI unit
  • In order not to let the numerical value become too large or too small, it is possible to replace a decimal factor with a prefix. These are listed in the Tabelle ##.

Example for calculating the power

physical equations

  • Physical equations enable physical quantities to be linked
  • There are two types of physical equations to be distinguished:
    • Equations of size
    • standardized size equations (also called related size equations)

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Equations of quantities

The vast majority of physical equations result in a physical unit that is not equal to $ 1 $.