THERMIONIC EMISSION Emission this is the process whereby electrons are emitted (given out) from a substance. Electron emission this is the process of liberating electrons from the metal surface.                    WAYS OF EMITTING ELECTRONS There are four ways of emitting electrons which are: THERMIONIC EMISSION Is the process of emitting electrons by applying heat energy.  OR is the discharge of electrons from the surfaces of heated materials. PHOTO ELECTRIC EMISSION Is the process of emitting electrons by application of light energy. HIGH FIELD EMISSION Is the process of emitting electrons by application of electric field. SECONDARY EMISSION Is the process of producing electron by application of highest speed field.  

1. THERMIONIC EMISSION
Emissionthis is the processwhereby electronsare emitted (givenout) from
a substance.
Electron emissionthisis the process of liberating electronsfrom the metal
surface.
WAYS OF EMITTING ELECTRONS
There are four ways of emitting electrons which are:
 THERMIONIC EMISSION Is the processof emitting electronsby
applying heat energy. OR is the dischargeofelectrons from the
surfacesof heated materials.
 PHOTO ELECTRIC EMISSION Is the process of emitting
electrons by applicationoflight energy.
 HIGH FIELD EMISSION Is theprocess of emittingelectronsby
applicationof electric field.
 SECONDARY EMISSION Is the processof producing electronby
applicationof highest speed field.
GENERAL MEANING OF THERMIONIC EMISSION
At the room temperature, metalconsist ofelectron which canmove around
a response to an applied electromagnetic field. Under normal condition, the
negativechargesof the electronare cancelled out by the positivechargesin
the atom of the metal. If metalis heated theelectron gainkinetic energy
and canleap out of the metal surfacetothe surrounding. Thisphenomena
is referred to as thermionic emission
Thermionic emissionisthe dischargeofelectrons from the surfaceof
heated materials. Thisprocesstakesplace in a tubecalled CATHODE
RAY TUBE
CONDITIONSFOR THERMIONIC EMISSION
1. The tubemust be highly evacuated i.e. low press.

2. 2. The cathodemust be hot.
3. Theremust be Anode which is positiveand cathodewhich is negative.
CATHODE RAY
Cathoderay is a stream of fast moving electron. The electron move in a
specific direction
Cathoderays
THE CATHODE RAY OSCILLOSCOPE (CRO)
CRO is a substanceor tubein which of cathode rays are produced.
Cathoderays oscilloscope is a vacuum tube containing electrongun,
deflectionsystem and fluorescent screen. These have internaland external
way of accelerateand deflect electronbeam that used to form imageinform
of light emitted and from fluorescent screen.

3. 1. ELECTRON GUN
It acceleratesand focuses electronsto the screen.
It comprises of;
(a)Grid – control the number of electron emitted.
(b)Cathode –for electron emitted.
(c)Anode – Acceleratesand focuselectrons to the screen.
The following are the functionsof the componentsof cathoderaytube:
1. Cathode
Thisis a metal filament such as tungstenthat is heated to high
temperatureseither directlybyan electric current or directlyheating
element. The temperatureof cathodecanrangecanrangefrom 800oC to
several thousandsdegree Celsius. At these high temperaturessomeof the
valence electrons in the metalattainenough kinetic energyto escapethe
cathodeby thermionic emission. Thecathodeismaintainedat negative
voltage.
2. Anode
Thisis a metal diskmaintained at a high positivevoltage(5000v –
50000v). Theanode acceleratestheelectrons ejected from cathode. There
are small opening in the anode through which a narrow beam of electrons
passes and enters a regionwhere their directioncanbe altered.
3. Horizontal deflection plates
These are twoparallel metalplates carrying equalbut oppositecharges.
They are used to deflect electrons beam horizontally (Left or Right). The
beam is attracted tothepositiveand negativeplateand repelled from the
negativeplate.

4. 4. Vertical deflection plates
These are similar tothe horizontaldeflectionplates but oriented to
deflect thebeam vertically(up or down). The horizontaland vertical
deflectionplates candirect thebeam towardsany point on the screen.
5. Fluorescentscreen
Thisis displaycomponent of the CRT. It is phosphoruscoated so that it
emitslight wherever the electronsstrike it.
The deflectionplates move the electronsbeam to different points on the
screen resulting in theformationof an image.
1. DEFLECTIONSYSTEM
It controls the deflectionof electronsin wrong ways
It comprise of;
(a) Timebaseit measurethe wave forms
(b)Terminalvoltage
 Magnetic field like pictures
 Electricalfield which aresound

5. (c)Horizontalplatey - They deflect electron verticallyupward and
verticallydownward
(d)Verticalplatex - They deflect electrons horizontally.
(e)Fluorescent screen
 Gives bright light on thespot
 For displaying signals
PROPERTIESOF CATHODE RAY OSCILLOSCOPE
1. Travel in a straight lineand they cast shadow.
2. They carrya negativecharge.
3. They have energy and momentum.
4. They causesfluorescence (grow) when they strikea materials.
5. They are deflected by electric field and magneticfield.
6. They ionize the gasif potentialdifferenceis high and gaspressure is
not high.
7. They penetrateinthin sheet of paper or metal foil depend on their
energy.
8. They affect photographicfilm.
9. They producex ray when stopped suddenly.
Application ofthe cathode ray tube
The cathoderaystubeis used in computer display, cathodetelevisionand
cathoderayoscilloscopes
1. It can be used as a voltmeter to measurevoltage
2. Display waveform
3. to measuretimeintervals
4. To measurephase relationship
5. Comparisonof frequencies
Televisionsand Computer Monitors

6. In television sets and computer monitors, theentirefront area of thetube is
scanned repetitivelyand systematicallyina fixed patterncalled a raster. An
imageisproduced by controlling the intensityof each of the three electron
beams, one for each additiveprimarycolor (red, green, and blue) with a
video signalas a reference. In all modern CathodeRay Tube( CRT)
monitorsand televisions, the beamsare bent by magnetic deflection, which
is a varying magnetic field generated bycoils and drivenby electronic
circuitsaround theneckof the tube
Monochrome Computer CRT Monitor
Monochromemonitor - thisCRT uses only one type of phosphor. Although
a mainstayof displaytechnologyfor decades, CRT-based computer
monitorsand televisions constitutea dead technology. The demand for
CRT screens has dropped precipitouslysince2000, and thisfall off has
been acceleratinginthe latter half of that decade. The rapid advancesand
falling pricesof LCD flat panel technology, first for computer monitorsand
then for televisions, has been the key factor inthe demiseof competing
displaytechnologiessuch as CRT, rear-projection, and plasma display.
Oscilloscope
An oscilloscope is a devicethat measures and displays voltages asa
timeversus voltage graph. Thevoltage differencebetweenthe positiveand
negativeprobeleads is measured, buffered, and displayed on thescreen as
a continuouscurve. Oscilloscopes aregenerally used to see if a circuit is
performing asexpected, but oscilloscopesare also useful for comparing
different signalsto each other
OscilloscopeDisplay
Exampleof an analog oscilloscope displayShown is a Lissajousfigure,
showing a harmonic relationship ofone horizontal oscillationcycleto three
verticaloscillationcycles.
Manyoscilloscopes also use CRT displays, though LCD displays are
becoming morecommon. In oscilloscopeCRTs, electrostatic deflectionis
used, rather thanthe magnetic deflectioncommonlyused with television
and other large CRTs. The beam is deflected horizontally by applying an
electric field betweena pair of plates to itsleft and right, and vertically by
applying an electric field to plates above and below.

7. Oscilloscopes uses electrostaticrather thanmagnetic deflectionbecausethe
inductivereactantofthe magnetic coilswould limit thefrequencyresponse
of theinstrument. Thecolor of the oscilloscope phosphor is much less
important thaninthecase of color televisionsor computer monitorssince
the primarypurposeisto evaluate signalvoltages rather thanconstruct
complex images; however, the persistenceof the phosphor maybe more
important. Phosphorsareavailablewith persistenceranging from less than
one microsecond toseveral seconds. For visual observationof brief
transient events, a long persistencephosphor maybe desirable. For events
which are fast and repetitive, or high frequency, a short-persistence
phosphor is generally preferable.
X – RAYS
X-radiation(composed ofX-rays) is a form of electromagneticradiation.
Most X-rayshave a wavelength in the rangeof 0.01 to 10 nanometers,
corresponding tofrequenciesin therange 30 petahertzto30 exahertz
(3×1016 Hz to 3×1019 Hz) and energiesin the range100 eV to 100 keV. X-
ray wavelengthsare shorter thanthose of UV rays and typicallylonger than
those of gamma rays.
X – Rays areelectromagneticradiationwhich produced whencathoderay
stopped rapidlyby hard object. X – Rays arereflected rays when cathode
ray hits(falls) the metaltarget.
THE X – RAYS RESULT FROMTWO PROCESSNAMELY
1. The rapid slowing down of electron as they enter the target Atom.
2. The excitationofthe target Atom.
X – Rays is a reflected rays when the cathoderayshits(falls) the metal
target. X – Rays areproduced x – rays tube.
CONSIDER THE DIAGRAM BELOWOF THE X – RAYS TUBE
BELOW

8. Alternative diagram
X – RAYS TUBE CONSIST OF;
1. Heater – produceheat.
2. Glass tube – evacuated glasstubeto keep out gasmolecules.
3. Concave cathode – focusing cathoderays(electron) to a spot on tangent.
4. Cooling firm – To remove much of theheat conducted along the thick
copper rod.
5. Tungstentarget – A target inwhich itsatom when strike by electrons
excited after absorbingK.E and converted into x – rays radiation.

9. 6. Copper rod – conduct heat awayfrom the target.
HOW X – RAYS TUBE ARE PRODUCED
X-raysare produced whenelectrons beam strikea metaltarget. The
electrons areliberated from the heated filament and accelerated bya high
voltage towardsthemetaltarget. TheX-raysare produced when the
electrons collide with the atomsand nuclei of the metaltarget.
The anode is maintained at high potentialsoas electrons acceleratesat the
speed necessaryto producethex – rays. Only small fractionofK.E of the
electrons becomesX – Rays radiationtherest is absorbed by thetarget
which becomeshot.
PROPERTIESOF X – RAYS
1. They penetratethrough substancebut absorbedmoreby dense solid.
2. Affect photographicfilm.
3. Ionize gases(so that thegases becomeconductor).
4. Not deflected by magnetic or electric field.
5. Carryno charges(neutral).
6. The speed of X – rays is 3 x 108m/stogive a moreintense beam of x –
rays the cathodemust bemade hotter to givemore electrons and give
more x – rays.
TYPES OF X – RAYS
X – Rays have wavelengthsbetween10-8M to 10-1 0M withinthisrangewe
canget two types of X – raysdue to different in wavelength and frequency
these are:
1. hard x ray and
2. soft x ray
1. SOFT X – RAYS

10. Thisis theone which have long wavelength but lower rangeof frequency.
Soft x rayproduced by lower voltage and hasless penetratingpower.
 Have longer wavelength (10-8M) e.g. TV set emit small amount of soft
rays.
2. HARD X – RAYS
Thisis theone which have got short wavelength high rangeof a frequency.
Produced with high voltageand has high penetrating power.
- Have short wavelength (10-1 0M).
Uses of x – rays
x – Rays finds manyapplicationsinhospitalsindustriesevenin scientific
research:
1. Medical practice
 To detect broken teeth or bones
 With casex – rays can be used to kill cancer cells and tumour cells
2. In industries
 To detect the brokenpart of a machines
 x – rays machinesareused to reveal hiddenmetalflaws
 x – rays are used to reveal defects in steel
plates
3. In scientific research
 x – rays microscopeshavemadeit possible to studythe arrangement
of possibleto study the arrangement ofthe molecules of crystalline
substance
4. In agricultural activities
5. In science and technology

11. HAZARDS/ EFFECTSOF X – RAYS
The part which get x – raysthe body tissues aredestroyed and kills cells
which causethe cancer cell one hard x – raysreduce 3 yrs of living.
X – Rays aredangerousto us becauseuse our bodies absorb theenergy
from x – rays radiationswhenbodiesabsorb thex – rays energy ions are
produced in thebody. These ions canchangeor destroy living cell. The
damagetothe body’s living cell can stop them from functioning and
multiplying which canlead to;
1. Cancer
2. Leukemia (blood cancer)
3. Hereditarydefectsin children
4. Death
PRECAUTIONS
People are thereforeadvised against exposing themselvesto X – Rays
unless it is absolutely unavoidable.