Chapter 12.1-12.3 CHEM 1B
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This 5 page Class Notes was uploaded by Stacy Vargas on Thursday October 1, 2015. The Class Notes belongs to CHEM 1B at University of California - Santa Cruz taught by Roberto Bogomolni in Fall 2015. Since its upload, it has received 43 views. For similar materials see CHEM 1B in Chemistry at University of California - Santa Cruz.
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Date Created: 10/01/15
121 Electromagnetic Radiation Electromagnetic Radiation ER is one of the ways energy travels This type of radiation has this name because electrical and magnetic elds simultaneously oscillate in planes mutually perpendicular to each other Characteristics of waves wavelength frequency and speed is the distance between 2 consecutive peaks or troughs in a waveas shown in the image below it is represented in the Greek letter lambda A o The units of wavelength will always be nanometers nm or meters m l secundl WE 4 cyclesfsemnd 4 hertz w 8 cyclesfsecund 8 hart EL is W3 2 l6 cyclesfsecunsd lv hertz the number of waves or cycles per second and is represented by the Greek letter nu v o The units used for frequency is hertz hz All types of ER travel at the speed of light however shortwavelength radiation has the highest frequency In the equation above c represents the speed of light which will be de ned as 299 x 10 8 ms A is your wavelength which is in meters and v is your frequency The image below shows the classi cation of ER Radiation provides important means of energy transfer Wavelength in meters 10 10 qu4gtltl f39gtlt10f lofl 10f I lit2 inf l quot l R l l i F 1 V n Gamma litrtmellet llnl fared lull1ettiill39En39ee Realme rays rage Ex 39 PM Simttweve HM Size eff r i r l 5 all l39 V 4 b I tquot lquot tremie g 7 nuclei Merrie Meleeulee Peper elip midi311 l 4x10 SXlni mumT fxlni 122 The nature of matter The term blackbody is used in this context to depict that radiation originates from thermal energy of the body only 0 Doesn t include radiation re ected from the object amp doesn t depend on the material composing the object Blackbody radiation is closely approximated by the radiation emitted through a tiny hole from a cavity inside an object v ZUDG tl l l 3008 5th Weeelehgth 11m classical Figure 124 n I theory of matter that predicts a radiation has no bleekbedly lhiete that the maximum maximum and goes to 39n nlte ehtfte te eherter wavelengths the IntenSIty at Very Short a a V wavelengths temperature Ie Increased an agreement 39 wiith the elbeewed ehengie from e 395 represented g V g I by h and has the value of 6 626 X reddleh to e white QIOW ee iren ie 10A34 Joules J S The heated te higher temperatures Change in energy AE is represented by the equation 0 where n is an integer h is Planck s constant and v is the frequency of the ER absorbed or emitted small quotpacketsquot of energy that can be transferred only in discrete units of size hv stream of quotparticlesquot viewed in ER Energy of each photon is expressed in the following equation h by i Ephetem where h is Planck s constant v is the frequency of the radiation and A is the wavelength of the radiation when electrons emit from the surface of a metal when light strikes it Characteristics of Photoelectric effect 1 No electrons are emitted by a given metal below a speci c frequency vO 2 Light with frequency lower than threshold frequency no electrons are emitted regardless of the intensity of the light 3 Light with frequency greater than threshold frequency the of electrons emitted increases with the intensity of the light 4 Light with frequency greater than threshold frequency the kinetic energy of the emitted electrons increases linearly with the frequency of the light Minimum energy required to remove electron EO hvO because a photon with less energy than EO vltv0 can t remove an electron light with frequency less than the threshold frequency produces no electrons Light where vgtvO the energy in excess of that required to remove electron is given to the electron as kinetic energy KE ea 12K KEElECEt GtTI 2 my by but it t t Mates of Veloeity Energy of Energy required electron of igneiclent to remove electron electron photon from metalis aptfaee A greater intensity means that more photons are available to release electrons To represent the relationship between 1 mass and energy Einstein rearranged quot L the famous E mcquot2 equation to E E l fg the following 2 w 0 w 6 0 t R FiglMaee Speed of light Elect on i log WMM W WW wave properties and particulate prop ertilee The energy ot eaoh photon of I Mass the radiation lie rellateel to the wave 395 a form Of energy llerlgth and frequenoy by the equation PhOtonS 0390 0t GXh39b39t mass and are E 2m 2 was not affected by gravity however a WW photon is in no sense a typical particle Photon has mass in a relativistic sense it has no rest mass Louis de Broglie derived the following relationship for the wavelength of a particle with momentum mv Broglie s equation
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