Sometimesitisusefultoknowtherealsizeorlengthofanobject.Ineverydaylifewecangetoutarulerandmeasureitdirectly.Thesizecanthenberecordedeitherasmeters,centimetersormillimeters,orasfeetandinches.
MicrometersOncetheobjectgetstobeverysmallthough,itisnecessarytomovetoadifferentkindofmeasurement.Insteadofmillimeterswemeasureinthousandsofamillimeter.Suchatinydivisioniscalledamicrometer.Itisgivenaspecialsymbol:µ,meaningmicro.Sowhen1µmisseen,wereadthisasonemicrometer.
NanometersTherearesmallermeasurestoo.Justlikethereare1000µmin1mm,thereare1000nanometers(nm)in1µm.Whenwewanttomeasurethesizeofanobjectshowninamicrograph(photographtakenusingamicroscope),wehavetorelyonthebarshownatthebottomoftheimage.Findthewhitebarsinthemicrographswithanumberattheend.Thecoloredimageisofabutterflywingseenthroughalightmicroscope.Noticethatthebarreads1mm.Thegreyimageisofonewingscaleseenusingascanningelectronmicroscopeathighmagnification.Thebaronthisimagereads1µm.CalculatingsizeTocalculatetherealsizeofthewingscalesinthetopimageweeithermeasureitonscreenoritmightbeeasiertoprintoutthissheet.Firstmeasurethelengthofthewhitebar(ontheprintedpage).Thiscomestoabout43.5mmdependingonyourprinter.Next,notethereallengthofthewhitebar,whichis1mm(thenumbernexttothewhitebar).Then,measurethewidthofaloosewingscale.Thiscomestoabout1.9mm(ontheprintedpage)again,dependingonyourprinter.
Nowcomesthepartwhereweworkouthowwidethatwingscalereallyisintherealworld.Multiplythewidthofthewingscaleinmillimeters(1.9mmorwhateveryoumeasure)bythesizethebartellsusisitsreallength(1mm).Dividetheanswerbythelengthofthebarinmillimeters(43.5mmorwhateveryoumeasure)togettherealwidthofthewingscale:
(1.9x1)/43.5=0.044mm.Ifwemultiplythisnumberby1000,itgivesusthesizeinmicrometers:
44µmTrythismethodwiththeSEMmicrographofabutterflywingscaleinthebottomimage.Calculatehowfarapartthelongridgesareonasinglebutterflyscale.Sincethebarisabout11mmlongontheprintedimage,andthisequalsarealworldlengthof1µm,andtheridgesareabout17.5mmapartontheprintedimage,theanswershouldbethattheridgesarereally1.59µmapart.Notethatthebarisusuallyreferredtoasascalebar,meaningthatitscalesupordowndependingonwhetherapictureisenlargedorreducedinsize,alwaysremainingaccurate.Inthiscontexttheword‘scale’hasnothingtodowithwingorfishscales.YouhaveagoHereisanotherexamplethatisnotworkedthrough.Calculatetherealsizeofthispollengrainfromyellowclover,intheSEMmicrographbelow.Youshouldgetananswerinmicrometers.Howmanyofthesepollengrainswouldfitintoasinglemillimeter?InternetresourcesThisisavideothatshowshowtocalculaterealsizefromanimageusingthebar:https://www.youtube.com/watch?v=5h5IFY-PYRw
