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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 described below.
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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. For example, input 50 kN m, or 50 kN⋅m, as follows:<br>
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| <pre style="font-size:113%;">50 kN m</pre>
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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.For example, input 10 m/s, or 10 m s<sup>-1</sup>, as follows:<br>
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| <pre style="font-size:113%;">10 m/s</pre> or <pre style="font-size:113%;">10 m s^(-1)</pre>
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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)).For example, input 4.7 m<sup>2</sup>, as follows:<br>
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| <pre style="font-size:113%;">4.7 m^2</pre>
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| * Parentheses are required when there is a risk of misinterpretation. For example, '''do not input 8 kN m^-2''' but rather:
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| <pre style="font-size:113%;">8 kN m^(-2)</pre>
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| * Permutations of the unit symbols are allowed. For example, the following two entries are considered identical:
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| <pre style="font-size:113%;">3 m kg s^(-2)</pre> or <pre style="font-size:113%;">3 kg m/s^2</pre>
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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<br><span style="font-weight:normal">Input from either column is acceptable</span>
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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<br><span style="font-weight:normal">Input from either column is acceptable</span>
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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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| ==Combined units==
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| Under each '''Part _''' on the '''Formulas question''' page, define '''Unit''' as single and combined units separated by <span style="font-family:monospace;font-size:113%;">=</span>. For example:
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| <pre style="font-size:113%;">Pa = N/m^2 = m^(-1) kg s^(-2)</pre>
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| ==SI Prefixes==
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| The '''SI''' and '''Formulas question''' prefixes are given in the table below. The only difference between the two systems is that the prefix micro is written μ in the SI but entered as u in the Formulas question.
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| {| class="nicetable"
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| |-
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| ! Factor
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| ! Name
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| ! SI symbol
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| ! Formulas question<br>input
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| !
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| ! Factor
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| ! Name
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| ! SI symbol
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| ! Formulas question<br>input
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| |-
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| | 10<sup>1</sup>
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| | deca
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| | da
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| | da
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| | 10<sup>-1</sup>
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| | deci
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| | d
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| | d
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| |-
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| | 10<sup>2</sup>
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| | hecto
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| | h
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| | h
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| | 10<sup>-2</sup>
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| | centi
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| | c
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| | c
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| |-
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| | 10<sup>3</sup>
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| | kilo
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| | k
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| | k
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| | 10<sup>-3</sup>
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| | milli
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| | m
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| | m
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| |-
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| | 10<sup>6</sup>
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| | mega
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| | M
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| | M
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| | 10<sup>-6</sup>
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| | micro
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| | μ
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| | u
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| |-
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| | 10<sup>9</sup>
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| | giga
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| | G
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| | G
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| | 10<sup>-9</sup>
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| | nano
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| | n
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| | n
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| |-
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| | 10<sup>12</sup>
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| | tera
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| | T
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| | T
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| | 10<sup>-12</sup>
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| | pico
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| | p
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| | p
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| |-
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| | 10<sup>15</sup>
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| | peta
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| | P
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| | P
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| | 10<sup>-15</sup>
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| | femto
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| | f
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| | f
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| |-
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| | 10<sup>18</sup>
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| | exa
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| | E
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| | E
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| | 10<sup>-18</sup>
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| | atto
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| | a
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| | a
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| |-
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| | 10<sup>21</sup>
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| | zetta
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| | Z
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| | Z
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| | 10<sup>-21</sup>
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| | zepto
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| | z
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| | z
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| |-
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| | 10<sup>24</sup>
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| | yotta
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| | Y
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| | Y
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| | 10<sup>-24</sup>
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| | yocto
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| | y
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| | y
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| |}
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| ==Assigning prefixes to units==
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| Prefixes can be assigned to units. Specify the unit followed by a list of the prefixes. For example:
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| <pre style="font-size:113%;">W: k M G T;</pre>
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| is equivalent to <span style="font-family:monospace;font-size:113%;">1 W = 1e-3 kW = 1e-6 MW = 1e-9 GW = 1e-12 TW</span>.
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| ==Conversion rules==
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| Conversion rules allow students to use alternative units.
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| ===Common conversion rules===
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| Under '''Extra Options''' on the '''Formulas question''' page, for / [Global - Basic conversion rules], select '"Common SI unit"' in order to use predefined common SI units conversion rules. With this setting, the following answers are equivalent:
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| <pre style="font-size:113%;">
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| 5 s
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| 5000 ms
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| 5e9 ns
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| </pre>
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| <pre style="font-size:113%;">
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| 0.2 m/s
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| 200 mm/s
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|
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| </pre>
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| <pre style="font-size:113%;">
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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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| </pre>
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| Select '''None''' if the '''Common SI unit''' contradicts your custom rules.
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| ===Custom rules===
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| The conversion of single units can be specified by equating their values. For example:
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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="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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| See the file '''conversion_rules.php'''.
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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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| [https://docs.moodle.org/33/en/Formulas_question_type < Formulas question type]
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