Chapter 4 ELECTRONICS4.1UNDERSTANDING THE USES OFCATHODE RAY OSCILLOSCOPEA student is able toexplain thermionic emissiondescribe the properties of cathode raysdescribe the or!in" principle of the cathode ray oscilloscopemeasure potential di#erence usin" the CROmeasure short time inter$als usin" the CROdisplay a$e forms usin" CROsol$e problems based on the CRO display4.1CATHODE RAY OSCILLOSCOPE4.1CATHODE RAY OSCILLOSCOPE4.1CATHODE RAY OSCILLOSCOPE4.1CATHODE RAY OSCILLOSCOPEThermionic EmissionInside a metal% a lar"e number of electrons is free to mo$e around&4.1CATHODE RAY OSCILLOSCOPEThermionic EmissionThe electron cannot escape from the surface because they are held bac! by the attracti$e forces of the atomic nuclei near the surface&4.1CATHODE RAY OSCILLOSCOPEThermionic Emission'oe$er% hen the metal is heated% some of its electrons may "ain enou"h thermal ener"y to escape from its surface&4.1CATHODE RAY OSCILLOSCOPEThermionic EmissionThe emission of electons fom t!e s"f#ce of # !e#te$ met#l is !no as thermionic emission&4.1CATHODE RAY OSCILLOSCOPECathode RaysThermionic emission is used to produce a continuous supply of electrons& These electrons can be made to mo$e at a hi"h speed in a $acuum tube& 4.1CATHODE RAY OSCILLOSCOPECathode Rays(hen a hi"h $olta"e is applied beteen the cathode and anode% the electrons are accelerated at a hi"h speed from the cathode to the anode&4.1CATHODE RAY OSCILLOSCOPECathode RaysThis beam of electrons hich mo$es at a hi"h speed is called cathode rays&4.1CATHODE RAY OSCILLOSCOPE4.1CATHODE RAY OSCILLOSCOPE%#ltese Coss T"&eA )altese Cross tube is a special cathode ray tube used to in$esti"ate the properties of cathode rays&4.1CATHODE RAY OSCILLOSCOPE%#ltese Coss T"&eThe )altese Cross bloc!s the beam of cathode rays and casts a shado on the screen& 4.1CATHODE RAY OSCILLOSCOPE%#ltese Coss T"&eThe )altese Cross bloc!s the beam of cathode rays and casts a shado on the screen& This indicates that cathode rays travel in straight line and they can be stopped by a piece of metal&4.1CATHODE RAY OSCILLOSCOPE%#ltese Coss T"&e*rocedure Obser$ation Explanation Conclusion+, heater supply is connectedA shado of the cross is seenThe shado is formed by the ray from the heated -lamentLi"ht rays tra$el in a strai"ht line4.1CATHODE RAY OSCILLOSCOPE%#ltese Coss T"&e*rocedure Obser$ation Explanation Conclusion+, heater supply and . !, poer supply are connectedThe "reen shado of the cross is seen same si/e and at the same position as the shado form by the li"htThe shado isformed by the cathode raysCathode rays tra$el in a strai"ht line&Cathode rays cause 0uorescence&Cathode rays carry !inetic ener"y and con$erts to li"ht ener"y hen they hit the screen&4.1CATHODE RAY OSCILLOSCOPE%#ltese Coss T"&e*rocedure Obser$ation Explanation ConclusionA bar ma"net is brou"ht close to the cathode raysThe cathode ray shado is mo$ed and distortedThe catapult force is produced because and the cathode rays carry a char"eCathode rays can be de0ected by ma"netic -elds& The 1lemin"2s left3hand rule is used to determine the direction of motion&Properties of Cathode RaysThese rays ori"inated from the cathode4 therefore% they are beams of ne"ati$ely char"ed particles called electrons&They tra$el in strai"ht line and cast sharp shados&They ha$e ener"y and can do or!&They are de0ected by ma"netic -eld and electric -eld&4.1CATHODE RAY OSCILLOSCOPEExample 5The dia"ram shos is applied to a cathode ray motion&(hat is direction of the cathode ray is shifted64.1CATHODE RAY OSCILLOSCOPEC#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEA C&R&O& is an instrument that con$erts electronic and electrical si"nals to a $isual display&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPE. main parts7 Electron gun, defection system and fuorescent screen&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEElectron gunThe electron "un consists of a heated cathode% a control "rid% a focusin" anode and an acceleratin" anode&The cathode is heated by heatin" -lament and emits a cloud of electrons&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEControl GridThe control "rid hich is placed o$er the emittin" surface of the cathode is used to control the number of electrons that ill pass throu"h it&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEFocusing AnodeThe focusin" anode hich is connected to a positi$e potential attracts the electrons from the control "rid and focuses the electrons into a beam&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEAccelerating AnodeThe acceleratin" anode is used to accelerate the electrons toards the screen&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEDefection ystemThe de0ection system consists of to sets of parallel plates% X 8hori/ontal9 and Y 8$ertical9&The function of Y3plate is to de0ect the electron beam $ertically 8up or don9 across the screen hen an input $olta"e is applied across it&The function of X3plate is to de0ect the electron beam hori/ontally 8left or ri"ht9 across the screen at a steady speed&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEFluorescent creenThe 0uorescent screen is coated ith 0uorescent material such as /inc sulphide on its inside surface&(hen a beam of electrons stri!es the screen% the material becomes luminous% or "los and appears as a bri"ht spot on the screen&C#t!o$e R#' Oscillosco(e )C.R.O.*4.1CATHODE RAY OSCILLOSCOPEFluorescent creenElectrons ha$e !inetic ener"y& (hen an electron stri!es a screen% the 0uorescent coatin" con$erts the !inetic ener"y of the electron to li"ht ener"y&Ene+' Con,esion of electons in C.R.O.4.1CATHODE RAY OSCILLOSCOPEElectric current heats the -lament% hich in turn emits electrons&Electrical ener"y Li"ht ener"yEne+' Con,esion of electons in C.R.O.4.1CATHODE RAY OSCILLOSCOPEAn electric -eld across the anode and cathode accelerates the electrons toards the 0uorescent screen&Electrical potential ener"y 8eV9 :inetic ener"y of electrons 85;< mev 5&+ x 5?35@C and me> @ x 5?3.5!"E( )1 - 7313 192s m 10 96 . 410 910 7 10 6 . 1 2221 = ===vmeVvv m eVeeH#n$lin+ C.R.O.4.1CATHODE RAY OSCILLOSCOPE:nob ; sitch1unction ; controlOn;o# To on or o# the CROFrilliance To control the intensity of he bri"ht spotG3shift To adHust the hori/ontal position of the bri"ht spotI3shift To adHust the $ertical position of the bri"ht spotI3"ain To ampli-ed the small $olta"e across the I3plates to de0ect the electron beam& The control is calibrated in $olt per cmTime3base controlsConnected to the G3plates to control the freJuency at hich the beam seeps hori/ontally across the screen& The control is calibrated in time per cmG3input To connect the source of potential di#erence to G3platesI3input To connect the source of potential di#erence to I3platesAC;CC sitchSelected accordin" to the type of input recei$edUses of C.R.O. - Dis(l#'in+ .#,e foms4.1CATHODE RAY OSCILLOSCOPEUses of C.R.O. - To %e#s"e Potenti#l Di/eence4.1CATHODE RAY OSCILLOSCOPEA beam of electrons is shot don an e$acuated tube by an electron "un& This beam passes beteen to sets of de0ectin" plates and then stri!es a screen that "los hen the beam hits it 80uorescence9&4.1CATHODE RAY OSCILLOSCOPE5& The CRO is sitched on& H cm+& The Y3"ain settin" is recorded > Y $olt;cmB& The potential di#erence across the dry cell is calculated % V > YH $oltUses of C.R.O. - To %e#s"e Potenti#l Di/eence4.1CATHODE RAY OSCILLOSCOPE5& The CRO is sitched on& x ms ; cmK& The time lapse beteen the to claps is calculated % t > x d msUses of C.R.O. - %e#s"in+ A S!ot Time Inte,#l4.1CATHODE RAY OSCILLOSCOPEThe dia"ram shos a a$eform obtained from an a&c& poer supply connected to I3input of a CRO&D I3"ain settin" >