Dual nature of radiation and matter

Dual nature of radiation and matter.

the phenomenon such as interference and diffraction ,polarization etc in which radiation interacts with radiation itself can be explained on the basis of electromagnetic(wave) nature of radiation only. the phenomenon such as photoelectric effect ,compton effect, pair production etc in which radiation interacts with matter can be explained on the basis of quantum (particle)nature of radiation only..

Electron Emmission. the ejection of electrons from the surface of metal is known as electron emission. we know that every metal has free electrons.These electrons are free to the extent that they may transfer from from one atom to the other within the metal but they cannot lethe metal surface to provide electron emission because of electrostatic attraction of positive nuclei inside the atom . However if sufficient energy is given to the free electrons their kinetic energy increases and thus electrons will cross over the surface barrier to leave the metal Work Function : the minimum energy required by an electron to just escape(i.e zero velocity) from metal’s surface is called work function of the metal. the work function of pure metals vary(roughly) from 2ev to 6ev 1ev =.

4. Methods of electron emmission. thermonic emission : In this method, the metal is heated to a sufficent temperature(about 2500 C) to enable the free electrons to leave the metal surface,the number of electrons emitted depends upon the temperature ,the greater is the emission of electrons the ejected electrons are called thermal electrons. Field emission : in this method ,a strong electrric field (ie a high positive voltage) is applied at the metal surface which pulls the free electrons out of the metal because of attraction of positive field,the strong the elctric field the greater is the emmision,the ejected electrons is called free electrons. Photoelectric emission: In this method the energy of the light the energy of light falling upon the metal surface is transfered to the free electrons within the metals to enable them to leave the surface .The greater the intensity of light beam falling on the metal surface the greater is the photoelectric emission the ejected electrons are called photoelectrons. Secondary emission: In this method a high velocity beam of primary electrons strikes the metal surface .The intensity of secondary emission depends upon the emitter material,mass and energy of bombarding particles the ejected electrons are called secondary electrons..

Effect of intensity of photoelectric current. current is the no of electrons passing through a cross section in unit time As intensity no of electrons increases current increase Photocurrent Intensity.

The phenomena of emission of electrons from a metal surface when radiations of suitable frequency is incident on it, is called photoelectric effect electrons emitted by this effect are called photoelectrons and the currentstituted by photoelectrons is known as photoelectric current or photocurrent. It was discovered by heinrich hertz in 1887 during EM Waves experiments.=NOTE Threshhold frequency = the minimum frequency of light which can eject photo electron from a metal surface is called threshold frequency of that metal. Threshold wavelength : the maximum wavelength rJ light which can eject photoelectron from a metal surface is called threshhold wavelength of that metal. Relation between work function threshold frequency and threshold wavelength.

Effect of collector potential. Collector potential is meant for collecting electrons current first increases with increase in collector potential after which it saturates ,it saturates when emitted electrons becomes equal to collected electrons.The maximum current is called saturated current. Now if we keep voltage negetive it will repel electrons.At some potential all electrons will get repelled . At this potential Photocurrent will be zero.This is called stopping potential eVstopping = KEmax = formula KEmax = hv - eVstopping = Stopping potential depends on frequency and work function..

Effect of frequency. For a fixed intensity of incident light , the photoelectric current does not depend upon the frequency of incident light saturation current will be the same for all frequencies>threshold frequency The graph between the frequency and stopping potential is a straight line and impies that there is always a minimum frequency below which there is a photocurrent..

1)For a given metal and frequency of incident light the photoelectric current(the reate of emission of photoelectrons) is directly proportional to the intensity of the incident light. 2) for a given metal there is a certain minimum frequency called threshold frequency below which there is no emission of photoelectrons takes.

Einstein’s photoelectric equation. 1)According to planck’s quantum theory light is emitted from a source in the form of bundles of energy called photon..

Einstein’s photoelctric equation. According to the law of conservation of energy , energy of photon = work function + kinetic energy imparted to electron.

Verification of laws of photelectric emission based on photoelectric equation.

Applications of photoelectric effect - Photocell.

Applications of photoelectric cells. Photoelectric cells are used in television camera for Telecasting scenes and also used in photo telegraphy It is used in counting machines photocells are used for sound recording and video recording it is used in burgler alarms and fire alarms photocells are also used to measure temperature of stars and study their spectrum They are also used to switch on or off the street light without any manual attention they are used in photometry to compare to compare the illuminating powers of the two sources they are used for determination of plancks constant they are used to controlthe temperature of chemical reactions they are used to sort out the materials of different shades they are used to determinethe opacity of solids and liquids they are used to obey minor flaws in metallic sheets.

Photons-Packets of energy. 1)Electrically neutral,No effect of electric field or magnetic field 2)Massless 3)energy = hv = hc/lambda and momentum = h/lamda 4)energy and momentum depends only on frequency or wavelength 5)When photon collides with the particle,then total momentum will remain conserved like any other normal collision,but some photons may die in collision (Number of photons change after collision) 6) All photons posess same energy irrespective of intensity of light .Increase in intensity only increases the no of photons.

De broglie wave. According to debroglie a moving material particle can be associated with a wave ie.a wave can guide a motion of the particle.the waves associated with the moving particles are known as debroglie waves or matter waves.

17. CONCLUSIO N = i)De broglie wavelength is inversely proportional to the velocity of the particle.If the particle moves faster ,Then the wavelength will be smaller and vice versa ii)If the particle is at rest then debroglie wavelength is infinite .Such a wave can not be visualised iii)debroglie wave length is inversely proportional to the mass of the particle.The wavelength associated with the heavier particle is smaller than that with a lighter particle. de broglie wavelength independent of the charge of the particle Matter waves like electromagnetic waves can travel in vaccume hence they are not mechanical waves. Matter waves are not electromagnetic waves because they are not produced by accelerated charges..

18. Davission and garner experiment. The davission and garner experiment was a physics experiment conducted by american physicists clinton davission and lester germer in 1927,which confirmed the de broglie hypothesis.This hypothesis advamnced by luis de broglie in 1924 states that particles of matter such as electrons have wave like properties .The experiment not only played in verifying de broglie hypothesis and demonstrated the wave particle duality but also was an important historical deveolopement in establishment of quantum mechanics and of the scrodinger equation. A beam of electrons emitted by the electron gun is made to fall on nickel crystal cut along cubical axis at particular angle.The scattered beam of electrons is recieved by the detector which can be rotated at any angle The energy of the incident beam of electronscan be varied by changing the applied voltage of the electron gun Intensity of scattered beam is found to be maximum when angle of scattering is 50 degree and the accelerating potential is 54 V..

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