Bir kap\u0131n\u0131n kendili\u011finden a\u00e7\u0131l\u0131vermesi, metrolardaki y\u00fcr\u00fcyen merdivenlerin inip \u00e7\u0131kmas\u0131, bir sinema filmindeki ses kayd\u0131n\u0131n okunmas\u0131, hep fotoelektrik lambalar\u0131n\u0131n (fotosel) \u00e7al\u0131\u015fmas\u0131yla ger\u00e7ekle\u015fir. Fotosellerin \u00e7al\u0131\u015fmas\u0131 ise, inan\u0131lmas\u0131 olduk\u00e7a g\u00fc\u00e7 fiziksel bir olaya, \u0131\u015f\u0131k arac\u0131l\u0131\u011f\u0131yla bir elektrik ak\u0131m\u0131n\u0131n \u00fcretilmesine dayan\u0131r.<\/p>\n
Telsiz telgraf\u0131n <\/a>ve radyonun geli\u015ftirilmesinde en \u00f6nemli \u015fey olan radyo dalgalar\u0131n\u0131\u00a0(elektromanyetik dalgalar) ke\u015ffeden\u00a0Heinrich\u00a0Hertz\u2019<\/strong>in 1887\u2019 de buldu\u011fu bu fotoelektrik olay\u0131, madde ile \u0131\u015f\u0131k aras\u0131nda enerji al\u0131\u015fveri\u015finin a\u00e7\u0131klanabilmesini sa\u011flam\u0131\u015ft\u0131r.<\/p>\n \u015eimdi \u015f\u00f6yle bir deney yapal\u0131m: Elektroskop ad\u0131 verilen ayg\u0131t, bir elektrik <\/a>y\u00fck\u00fcn\u00fcn varl\u0131\u011f\u0131n\u0131 ve \u00f6nemini saptamaya yarar; bu ayg\u0131t, iyice yal\u0131t\u0131lm\u0131\u015f metal bir \u00e7ubu\u011fun ucuna ikiye katlanarak ortas\u0131ndan as\u0131lan ince bir alt\u0131n yapraktan olu\u015fur; yaprak ile \u00e7ubuk, bir penceresi bulunan metal bir kafesin i\u00e7ine yerle\u015ftirilir. Metal \u00e7ubu\u011fun d\u0131\u015f ucuna bir elektrik y\u00fck\u00fc verildi\u011finde, alt\u0131n yapra\u011f\u0131n katlar\u0131 a\u00e7\u0131l\u0131r. Metal \u00e7ubu\u011fu bu kez iyice temizlenmi\u015f bir \u00e7inko levhaya ba\u011flay\u0131p, \u00e7inkonun y\u00fczeyini g\u00fc\u00e7l\u00fc bir \u0131\u015f\u0131kla ayd\u0131nlat\u0131rsak, elektroskobun elektrik y\u00fcklendi\u011fini g\u00f6r\u00fcr\u00fcz : \u00c7inko levhaya d\u00fc\u015fen \u0131\u015f\u0131k, bir elektrik y\u00fck\u00fc do\u011furmu\u015ftur.<\/p>\n Hertz\u2019in bu deneyi, \u00e7ok \u00f6nemli sonu\u00e7lara ula\u015f\u0131lmas\u0131n\u0131 sa\u011flam\u0131\u015ft\u0131r: Bir elektrik y\u00fck\u00fc, maddenin en k\u00fc\u00e7\u00fck bile\u015fenleri olan elektronlar\u0131n varl\u0131\u011f\u0131ndan ba\u015fka \u015fey olmad\u0131\u011f\u0131na g\u00f6re, \u0131\u015f\u0131\u011f\u0131n, bu elektronlar\u0131 maddeden, s\u00f6z konusu deneyde kulland\u0131\u011f\u0131m\u0131z \u00e7inko levhadan \u00abs\u00f6k\u00fcp almas\u0131\u00bb gerekir. Ayr\u0131ca, metalden bu elektronlar\u0131 koparmas\u0131 i\u00e7in, \u0131\u015f\u0131\u011f\u0131n belli bir enerji ta\u015f\u0131mas\u0131 zorunludur. Fotoelektrik olay\u0131, \u0131\u015f\u0131\u011f\u0131n, bir metaldeki elektronlar\u0131 s\u00f6k\u00fcp almak i\u00e7in gereken enerjiyi sa\u011flad\u0131\u011f\u0131n\u0131 g\u00f6sterir.<\/p>\n B\u00fct\u00fcn yal\u0131nl\u0131\u011f\u0131na kar\u015f\u0131n, olay son derece ilgi \u00e7ekicidir: Belli bir cisim, \u0131\u015f\u0131\u011f\u0131n ancak belli bir frekans\u0131nda elektron yaymaya ba\u015flar ve \u0131\u015f\u0131k kayna\u011f\u0131n\u0131n \u015fiddeti ne olursa olsun, yay\u0131mlanan elektronlar\u0131n h\u0131z\u0131 en y\u00fcksek de\u011fere ula\u015f\u0131r I\u015f\u0131k yaln\u0131zca bir titre\u015fim olsayd\u0131, yani bir dalga yap\u0131s\u0131 g\u00f6sterseydi, elektronlar\u0131n h\u0131z\u0131, bu dalga kayna\u011f\u0131n\u0131n \u015fiddeti y\u00fckseldik\u00e7e artard\u0131.<\/p>\n Bu olay\u0131n ilgi \u00e7ekici ve \u015fa\u015f\u0131rt\u0131c\u0131 \u00f6zelli\u011finden etkilenen Albert Einstein<\/strong>, 1905\u2019te bilim d\u00fcnyas\u0131nda devrim yaratacak bir a\u00e7\u0131klama yapt\u0131 : I\u015f\u0131k \u0131\u015f\u0131mas\u0131ndaki enerjinin kesikli k\u00fc\u00e7\u00fck par\u00e7ac\u0131klara, yani kuvantalara b\u00f6l\u00fcnd\u00fc\u011f\u00fcn\u00fc ve daha sonraki y\u0131llarda foton<\/strong> ad\u0131 verilen \u0131\u015f\u0131k taneciklerine y\u00fcklendi\u011fini \u00f6ne s\u00fcrd\u00fc. Bu fotonlar, \u0131\u015f\u0131n\u0131m frekans\u0131n\u0131n Planck de\u011fi\u015fmezi (sabiti) denilen \u00e7ok \u00f6nemli bir fiziksel de\u011fi\u015fmezle \u00e7arp\u0131m\u0131na e\u015fit bir enerji ta\u015f\u0131yarak \u0131\u015f\u0131k h\u0131z\u0131yla yer de\u011fi\u015ftirir.<\/p>\n Olaya bu bilgilerin \u0131\u015f\u0131\u011f\u0131 alt\u0131nda bak\u0131nca, \u0131\u015f\u0131k kayna\u011f\u0131n\u0131n \u015fiddeti de\u011fi\u015ftirilse bile bu \u0131\u015f\u0131k taneciklerinden hi\u00e7 birinin enerjisinde en k\u00fc\u00e7\u00fck bir de\u011fi\u015fiklik olmayaca\u011f\u0131, yay\u0131mlanan elektronlar\u0131n i\u015fte bu nedenle en y\u00fcksek h\u0131za ula\u015ft\u0131\u011f\u0131 anla\u015f\u0131l\u0131r. Einstein\u2019a Nobel \u00f6d\u00fcl\u00fc, ba\u011f\u0131ll\u0131k kuram\u0131n\u0131 geli\u015ftirdi\u011fi i\u00e7in de\u011fil, bu alandaki \u00e7al\u0131\u015fmalar\u0131 i\u00e7in verilmi\u015ftir.<\/p>\n Fotoelektrik olay\u0131n\u0131n bilinmesi, Broglie<\/strong>, Schr\u00f6dinger<\/strong> ve Heisenberg<\/strong>\u2019in de katk\u0131lar\u0131yla, \u0131\u015f\u0131\u011f\u0131n yap\u0131s\u0131na ili\u015fkin \u00e7a\u011fda\u015f bilgilerin geli\u015fmesinde \u00e7ok \u00f6nemli rol oynam\u0131\u015ft\u0131r.<\/p>\n S\u00f6z konusu olay, zamanla pek \u00e7ok uygulamaya konu oldu: Bu uygulamalar\u0131n en \u00fcnl\u00fcs\u00fc, fotosel lambalar\u0131d\u0131r<\/a>. G\u00f6r\u00fcn\u00fcr \u0131\u015f\u0131\u011fa tutulan bu lambalar, kolayca saptanabilen bir elektrik ak\u0131m\u0131 do\u011fururlar. Fotosellerde elektron yayan metal, sezyum, potasyum ya da sodyum olabilir. Ne var ki, kullan\u0131lan metal hangisi olursa olsun, fotoselin \u00fcretti\u011fi ak\u0131m \u00e7ok zay\u0131ft\u0131r; bu nedenle, fotonlar\u0131n varl\u0131\u011f\u0131n\u0131 saptamaya ve onlar\u0131 saymaya yarayan foto\u00e7o\u011falt\u0131c\u0131larda bu ak\u0131m\u0131 y\u00fckseltme yoluna gidilir.<\/p>\nAlbert Einstein<\/a><\/h2>\n
Broglie, Schr\u00f6dinger ve Heisenberg\u2019in de katk\u0131lar\u0131<\/h2>\n