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| [https://docs.moodle.org/33/en/Formulas_question_type < Formulas question type]
| | #REDIRECT [[Formulas:_Systems_of_units]] |
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| ==Writing unit symbols==
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| In the Formulas question type, the writing of the units differs slightly from that in the SI because units are entered very simply on the computer. The rules for entering units are as follows:
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| * The multiplication of unit symbols is indicated by a space, as prescribed in Section 5.1 of SI. The half-high (centred) dot (⋅) is not supported.
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| * Division of unit symbols is indicated by a solidus (oblique stroke, <span style="font-family:monospace;font-size:113%;">/</span>) or by negative exponents.
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| * Exponentiation is indicated by the circumflex accent (<span style="font-family:monospace;font-size:113%;">^</span>, UTF-8 <span style="font-family:monospace;font-size:113%;"><span style="font-size:165%;">﹠</span>#94;</span> or ASCII code 94 (alt+94)).
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| * Parentheses are required when there is a risk of misinterpretation.
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| * Permutations of the unit symbols are considered identical.
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| ==Units==
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| The system of units of the Formulas question type complies with the [https://www.bipm.org/en/publications/si-brochure/ International System of Units (SI)] (available free of charge). In the International System of Units (SI) units are classified as either base units or derived units ([https://www.bipm.org/en/publications/si-brochure/ SI]).
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| Units of the Formulas question type system of units are the same as those of the set of coherent SI units and as the units outside the SI.
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| There are seven base units in the SI:
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| {| class="nicetable"
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| |-
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| ! Name
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| ! Symbol
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| ! Formulas question type input
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| |-
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| | metre
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| | m
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| | m
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| |-
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| | kilogram
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| | kg
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| | kg
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| |-
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| | second
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| | s
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| | s
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| |-
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| | ampere
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| | A
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| | A
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| |-
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| | kelvin
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| | K
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| | K
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| |-
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| | mole
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| | mol
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| | mol
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| |-
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| | candela
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| | cd
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| | cd
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| |}
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| Coherent derived units are simple products of powers of base units. Some examples of coherent derived units are as follows:
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| {| class="nicetable"
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| |-
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| ! Name
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| ! Symbol
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| ! colspan="2" | Formulas question type input
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| |-
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| | square meter
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| | m<sup>2</sup>
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| | m^2
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| |-
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| | cubic meter
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| | m<sup>3</sup>
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| | m^2
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| |-
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| | meter per second
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| | m/s
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| | m/s
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| | m s^(-1)
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| |-
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| | meter per second squared
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| | m/s<sup>2</sup>
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| | m/s^2
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| | m s^(-2)
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| |-
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| | reciprocal metre
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| | m<sup>-1</sup>
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| | m^(-1)
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| |-
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| | kilogram per cubic metre
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| | kg/m<sup>3</sup>
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| | kg/m^3
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| | kg m^(-3)
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| |-
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| | kilogram per square metre
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| | kg/m<sup>2</sup>
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| | kg/m^2
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| | kg m^(-2)
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| |-
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| | cubic metre per kilogram
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| | m<sup>3</sup>/kg
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| | m^3/kg
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| | m^3 kg^(-1)
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| |-
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| | ampere per square metre
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| | A/m<sup>2</sup>
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| | A/m^2
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| | A m^(-2)
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| |-
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| | etc.
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| |}
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| Some coherent derived units have special names and symbols:
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| {| class="nicetable"
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| |-
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| ! Name
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| ! Symbol
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| ! colspan="3" | Formulas question type input
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| |-
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| | radian
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| | rad
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| | rad
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| | m/m
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| |-
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| | steradian
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| | sr
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| | sr
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| | m^2/m^2
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| |-
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| | hertz
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| | Hz
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| | Hz
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| | s^(-1)
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| |-
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| | newton
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| | N
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| | N
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| | m kg s^(-2)
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| |-
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| | pascal
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| | Pa
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| | Pa
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| | N/m^2
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| | m^(-1) kg s^(-2)
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| |-
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| | joule
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| | J
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| | J
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| | N m
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| | m^2 kg s^(-2)
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| |-
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| | watt
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| | W
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| | W
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| | J/s
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| | m^2 kg s^(-3)
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| |-
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| | coulomb
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| | C
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| | C
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| | s A
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| |-
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| | volt
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| | V
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| | V
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| | W/A
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| | m^2 kg s^(-3) A^(-1)
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| |-
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| | farad
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| | F
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| | F
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| |-
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| | ohm
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| | Ω
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| |-
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| | siemens
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| | S
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| | S
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| |-
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| | weber
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| | Wb
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| | Wb
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| |-
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| | tesla
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| | T
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| | T
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| |-
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| | henry
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| | H
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| | H
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| |-
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| | degree Celcius
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| | ℃
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| | ℃
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| |-
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| | lumen
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| | lm
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| | lm
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| |-
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| | lux
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| | lx
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| | lx
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| |-
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| | becquerel
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| | Bq
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| |-
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| | gray
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| | Gy
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| |-
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| | sievert
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| | Sv
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| |-
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| | katal
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| | kat
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| |}
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| The base and coherent derived units of the SI form a coherent set, designated the set of coherent SI units.
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| There are also units outside the SI. Non-SI units accepted for use with the SI are:
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| {| class="nicetable"
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| |-
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| ! Name
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| ! Symbol
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| ! Formulas question type input
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| |-
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| | minute
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| | min
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| | min
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| |-
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| | hour
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| | h
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| | h
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| |-
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| | day
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| | d
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| | d
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| |-
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| | degree (plan angle)
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| | °
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| |-
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| | minute (plan angle)
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| | ′
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| |-
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| | second (plan angle)
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| | ″
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| |-
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| | hectare
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| | ha
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| | ha
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| |-
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| | litre
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| | L, l
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| | L or l
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| |-
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| | tonne
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| | t
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| | t
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| |}
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| ==Marking==
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| The system of units allows to test students' knowledge of units. Alternative equivalent units are allowed.
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| You can specify mark fraction deduction for a wrong unit. The wrong unit here means that the unit that is not convertible to the correct unit, under conversion rules. Suppose a student get 2 marks for this subquestion answer. If the unit penalty = 0.2 and she give wrong unit, then the student can get 2(1-0.2) = 1.6 mark for this submission. (See Grading scheme).
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| If a teacher does not specify any unit for the subquestion, then the unit box will not be displayed and there is no need for students to enter it. However, if the student enters anything after their answer, it is usually considered to be incorrect so the mark of unit will be deduced. Hence, in the above case, it is better to set 1 for mark deduction.
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| Nevertheless, if you do not want to penalize the student entering arbitrary string at the end of answer, set 0 for mark deduction. i.e. their unit does not count toward their grade, but you still allow student use any convertible unit. Note that you have assumed a default answer that does not require unit.
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| ==Conversion rules==
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| Conversion rules allow students to use alternative units. (See UnitConversion for details.)
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| ====Other rules====
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| You can specify the conversion of the base unit by equating their values under different units. Examples:
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| <pre style="font-size:113%;">
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| 1 m = 100 cm = 1000 mm;
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| 1 cm = 0.3937 inch;
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| </pre>
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| With the above conversion rule, the following answers are equivalent:
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| <pre style="color:#f98012;font-size:113%;">
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| 10 inch
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| 25.4 cm
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| 254 mm
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| 0.254 m
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| </pre>
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| For the SI prefix, an alternative syntax can be used: base unit followed by a list of SI prefix name.
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| <pre style="color:#f98012;font-size:113%;">W: k M G T;</pre>
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| which is equivalent to <span style="font-family: monospace;color:#f98012;font-size:113%;">1 W = 1e-3 kW = 1e-6 MW = 1e-9 GW = 1e-12 TW</span>.
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| ===Basic conversion rule===
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| For the conversion between common SI unit with different prefix, there are a set of predefined conversion rules for them. The only thing you need to do is to choose the 'Common SI unit' in the 'Basic conversion rule'.
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| The following answers in the each group
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| 5 s
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| 5000 ms
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| 5e9 ns
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| 0.2 m/s
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| 200 mm/s
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| 1 m^2
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| 10000 cm^2
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| 1e-6 km^2
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| are all equivalent to each other. So if one of the answer is correct, all other are also correct answers.
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| Note that you may also use 'None' if you find it contradicting with your own rules. If you want to define you own, see the file conversion_rules.php.
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| Identifying composite unit: Note that, the base units and composite unit cannot be identified in the conversion rules above. To specify a list of allowable composite unit, you can use separator '=' in the 'Unit'. For example
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| N = kg m s^(-2)
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| It identity the unit Newton to its SI counterpart. Hence, both composite unit are correct.
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| [https://docs.moodle.org/33/en/Formulas_question_type < Formulas question type]
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