GCSE›Edexcel GCSE Physics›Mind mapsExpressing Quantities & SI UnitsEdexcel GCSE Physics: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat are SI units?Standard units agreed worldwideLet measurements be compared consistentlyDistance in metres (m)Mass in kilograms (kg)Time in seconds (s)Prefixesgiga (G) = ×109\times 10^{9}×109mega (M) = ×106\times 10^{6}×106kilo (k) = ×103\times 10^{3}×103centi (c) = ×10−2\times 10^{-2}×10−2milli (m) = ×10−3\times 10^{-3}×10−3micro (µ) = ×10−6\times 10^{-6}×10−6SI unitsquantities and unitsmkgsConverting unitsMultiply or divide by the conversion factor1 hour = 3600 s2.5 h = 2.5×3600=9000 s2.5 \times 3600 = 9000\,\text{s}2.5×3600=9000s1 km = 1000 mWriting numbersUse significant figures matching the dataUsually 2 or 3 significant figuresStandard form: A×10nA \times 10^{n}A×10n1 ≤ A < 10Speed of light = 3×108 m/s3 \times 10^{8}\,\text{m/s}3×108m/sExam tipsAlways give the unit with the answerRight number, wrong unit loses a markDo not mix up milli and micro