ATOMIC PHYSICS PREVIOUS EAMCET QUESTIONS ENGINEERING 9. Te work function of a certain metal is. J. Ten te maximum kinetic energy of potoelectrons emitted by incident radiation of wavelengt 5 A is: (9 E) ).48 ev ).4 ev ).7 ev 4).8 ev Ans : From potoelectric equation w + mv C mv w (. 4 )( 8 ) 9..4eV 5. An X-ray tube produces a continuous spectrum of radiation wit its sortest wavelengt of 45 x Ans: A. Te maximum energy of a poton in te radiation in ev is (. x 4 J-sec, c x 8 m/ssec) (8 E) ) 7, 5 ), 5 ) 7, 5 4), 5 min 45 A 4 8. Energy E 75 45 min. X-rays of energy 5KeV. are scattered from a carbon target. Te scattered rays are at 9 from te incident beam. Te percentage of cange in wavelengt (m e 9 - Kg, C 8 m/s.) (8 E) ) % ) % ) 5% 4) % Ans : E 4 8. m 9 5. 4. ( cos9 ) 8 mc 9 4. 8 7 Cange in wavelengt % 4. An electron beam travels wit a velocity of. x 7 ms perpendicularly to magnetic field of intensity. T. Te radius of te pat of te electron beam (m e 9 x kg) (7 E) ) 9 x 5 m ) 9 x m ) 9 x 4 m 4) 9 x m Ans : Centripetal force Magnetic force
Atomic Pysics mv Bqv r 7 mv 9. r 9 Bq.. 4 9 m 5. Te work function of nickel is 5eV. Wen ligt of wavelengt A falls on it, emits potoelectrons in te circuit. Ten te potential difference necessary to stop te fastest electrons emitted is (given.7-4 Js) [ 7 E] ).V ).75V ).V 4).75V Ans : 4 Wen wavelengt is expressed in A ten E ev ω ev +.ev 5eV + ev V.V. In an experiment on potoelectric emission from a metallic surface, wavelengt of incident ligt is x 7 m and stopping potential is.5v. Te tresold frequency of te metal (in Hz) approximately (carge of electron e. x 9 C, Plank s constant. x 4 JS) (7 E) ) x 5 ) 9x 5 ) 9 x 4 4) x Ans: v ev + 4 8. 9 4 ν eν.5. 9 7 7. An oil drop aving a mass 4.8 - g. and carge.4-8 C stands still between two carged orizantal plates seperated by a distance of cm. If now te polarity of te plates is canged te instantaneous acceleration of te drop is (in ms - ) (g ms - ) [ E] ) 5 ) ) 4) 4 Ans : Mass m 4.8 g 4.8 g 8 Carge q.4 C Distance d - m Wen te carge is balanced Eq mg Eq mg Wen te field is reversed F ma Eq + mg mg + mg mg a g ms
Atomic Pysics 8. A proton, a deutron ( nucleus of H ) and an α- particle wit same kinetic energy enter a region of uniform magnetic field moving at rigt angles to te field. Te ratio of te radii of teir circular pats is ( E) ) : : 4 ) : : ) : : 4) : : Ans : Proton H Deuteron α particle H He 4 Centripetal force magfnetic force mv qvb r p r qb Radius r mke m r qb q m m m r: r: r : : q q q 4 : : : : 9. A particle of mass x kg and carge. x 9 C travelling wit a velocity.8 x ms along te positive X-axis enters a region in wic a uniform electric field E and a uniform magnetic field of induction B are present. If E.4 knc ˆ and B 8 ˆ jwbm, te direction of motion of te particles is (5 E) ) along te positive X-axis ) along te negative X-axis ) at 45 to te positive X-axis 4) at 5 to te positive X-axis Ans : Sol : EB, are acting in Z, Y directions Here E B gives velocity of carge particle Te carged particle is not deviated. Ligt rays of wavelengts A and of poton intensity 9. watts/m is incident on a metal surface. If only one percent of potons incident on te surface emit poto electrons, ten te number of electrons emitted per second per unit area from te surface will be [ Planck constant.4 x -4 J - S; Velocity of ligt x 8 ms - ] [4E] ) x 8 ) x 8 ) x 7 4) x 5 Ans : E Number of electrons emitted per second per unit area from te surface n 4 Poton energy, υ nm.ev ( )
Atomic Pysics I 9. W/m 9. J/s/m 9. ev / s / m 9. Potoelectrons emitted/s/m 9. 7 9... is te difference between te wavelengt of Kα line and te minimum wavelengt of te continuous X-ray spectrum wen te X-ray tube is operated at a voltage V. If te operating voltage is canged to v/ ten te above difference is. Ten [4E] ) ) 4 ) 4) < Ans :.4 For continuous X-ray spectrum min ev k k x ev k k x ev / As k does not cange wit voltage and x/ev. k x k k x k x < <. Electrons ejected from te surface of a metal, wen ligt of certain frequency is incident on it, are stopped fully by a retarding potential of volts. Poto electric effect in tis metallic surface begins at a frequency x 4 s -. Te frequency of te incident ligt in s - is [ x -4 J-sec; carge on te electron. x -9 C ] [ 4E] ) 7.5 x ).5 x ) 4 x 4 4) 7.5 x 5 Ans: According to Einstein s Poto electric equation, v v + K. E v + ev ev v v + 4 v.5 Js. Matc te pairs in two lists given blew [ 4 E] List I List- II a) Spectra produced by ligt from d) Poton incandescent solid b) Elementary particles wit zero mass and wit e) Continuous spectra a spin of unity c) Potocell in wic current canges wit f) Poto-emissive cell 4
Atomic Pysics cange in intensity of ligt after gap g) Poto-conducting cell ) Neutrino i) Band spectra a) a-e, b-d, c-g ) a-i, b-, c-f ) a-e, b-, c-f 4) a-i, b-d, c-g Ans: Sol --- 4. Consider te two following statements A and B and identify te correct coice given in te answers: A) In potovoltaic cells, te potoelectric current produced is not proportional to te intensity of incident ligt. B) In gas filled potoemissive cells, te velocity of potoelectrons depends on te wavelengt of te incident radiation. ( E) ) Bot A and B are true ) Bot A and B are false ) A is true but B is false 4) A is false but B is true Ans: 4 Sol. A) According to te laws of potoelectric effect potoelectric current is proportional to intensity of incident ligt. 5. Wen radiation of wavelengt is incident on a metallic surface, te stopping potential is 4.8 volts. If te same surface is illuminated wit radiation of double te wavelengt, ten te stopping potential becomes. volts. Ten te tresold wavelengt for te surface is [ E] ) ) 4 ) 4) 8 Ans: Sol From Einsteins potoelectric equation : ev υ υ e 4.8.() e. 4.8e +.e.4e+.e.4e.8e.e.e.e /.4e.4 e / 4 4. Two potons of energies twice and trice te work function of a metal are incident on te metal surface. Ten te ratio of maximum velocities of te potoelectrons emitted in te two cases respectively is ( E) ) ) ) 4) 4 5
Atomic Pysics Ans :4 From Einsteins potoelectric equation v w + K. E K υ W K W W W K W W W But kinetic energy mv ν K W ν K W 7. In Compton scattering process, te incident Xradiation is scattered at an angle. Te wavelengt of te scattered radiation is.a. Te wavelengt of te incident X-radiation in A units is take.4a [ E] mc ).58 ).48 ). 4).8 Ans :4 From Compton effect ( cosθ) mc ( cosθ) mc..4( cosθ ).8A 8. If is te de Broglie wavelengt for a proton accelerated troug a potential difference of V, te de Broglie wavelengt for α-particle accelerated troug te same potential difference is [ E] ) ) ) 4) Ans: De-broglie wavelengt p mv m( K. E) p p mk mev p p p α mk α α 4mp ev α α 8 p 9. Potoelectric emission is observed from a metallic surface for frequencies v and v of te incident υ >υ. If te maximum values of kinetic energy of te potoelectrons emitted in te two ligt rays ( ) cases are in ratio of :k, ten te tresold frequency of te metallic surface is ( E)
kυ υ kυ υ kυ+ υ ) ) ) k k k Ans : Let te maximum energy of te potoelectrons be x and Kx x υ υ ( υ υ).() k x υ υ ( υ υ).() ( ) kυ υ υ k () 7 4) Atomic Pysics. Te de Broglie wavelengt of an electron aving 8 ev of energy is nearly (ev.x 9 J), mass of te electron 9 x kg), Planck s constant. x 4 Js) ( E) Ans :4 ) 4 A ).4 A ) 4 A 4).4 A de-broglie wavelengt me 5 5.7A ν 8. Wen a metal surface is illuminated by ligt of wavelengts 4 nm and 5 nm, te maximum velocities of te potoelectrons ejected are v and v respectively. Te work function of te metal is ( Plank s constant, c velocity of ligt in air) ( E) ) J ).5 J ) J 4).5 J Ans : Sol : W + mv.() 4 W + 4 mv 5.() From (), mv W 4 Substituting in equation () W + 4 W W 5 4 W ( ) J 5 MEDICAL. A poton of energy E ejects a poto electron from a metal surface wose work function is W. If tis electron enters into a uniform magnetic field of induction B in a direction perpendicular to te field and describes a circular pat of radius r, ten te radius r is given by (in te usual notation) : Ans :4 ) ( + ) m E W eb m E W eb ) ) ( ) ( ) m E W mb 4) ( ) m E W Be (9 E)
E w + mv ( ) E w v () m Atomic Pysics In te magnetic field, mv Be v r mv r.. () Be Substituting () in () m( E w ) r Be. Electrons accelerated by a potential of V volts strike a target material to produce continuous X- rays. Ratio between te de-broglie wavelengt of te electrons striking te target and te sortest wavelengt of te continuous X-rays emitted is (9 M) ) ) m ) Ve 4) Vem c Ve c m Ve m Ans : de-broglie wave lengt mv mev Sortest wavelengt mev ev ev ev c m 4. In Millikan s oil drop experiment, a carged oil drop of mass is eld stationary 4. kg between two parallel plates mm apart, by applying a potential difference of V between tem. How many electrons does te oil drop carry? (gms - ) (9 M) ) 7 ) 8 ) 9 4) Ans: 4 Under equilibrium mg Eq V mg d mgd n Ve n ( ne) ( 4 )( )(. ) 9 ( )(. ) 8
9 Atomic Pysics 5. An oil drop aving a carge was kept between two plates aving a potential difference of 4V is in equilibrium. Now anoter drop of same oil wit same carge but double te radius is introduced between te plates. Ten te potential difference necessary to keep te drop in equilibrium is ) V ) 8 V ) V 4) V (8 M) Ans :4 F Eq mg but v E d Vq mg d Vq 4 π R ρ g d V R V R V R 4 R V 8R ; V. Te tresold frequency for a certain metal is v. Wen a certain radiation of frequency v is Ans : incident on tis metal surface te maximum velocity of te potoelectrons emitted is x ms. If a radiation of frequency v is incident on te same metal surface te maximum velocity of te potoelectrons emitted (in ms ) is (8 M) ) ) ) 4 4) 4. ( ) K E v v v.() ( ) K. E v v v..() Dividing () and () mv mv V V V 7. Te velocity of te most energetic electron emitted from a metallic surface is doubled wen te frequency v of te incident radiation is doubled. Te work function of tis metal is (7 M) ) ν ) ν ) ν 4) ν 4 Ans: 4 v ω + mv.()
v ω + mv 4 () 4 4v 4ω + 4 () v ω + 4 mv..() mv Atomic Pysics -------------------------------------------------- v Substracting v ω ω 8. A proton and an alpa particle are accelerated troug te same potential difference. Te ratio of te wavelengt associated wit proton and alpa particle respectively is (7M) ) : ) : ) : 4) 4 : Ans : From de-broglie wavelengt mv mev mqv p p p : α mqv α α 9. In X-ray spectrum, transition of an electron from an outer sell to an inner sell gives a caracteristic X-ray spectral line. If we consider te spectral lines K β, L β and M α, ten ( M) ) K β and L β ave a common inner sell ) K β and L β ave a common outer sell ) L β and M α ave a common outer sell 4) L β and M α ave a common inner sell Ans : Sol. L β is transition from N to L M α is transition from N to M In bot of tem, te outer sell is same.. Te de-broglie wavelengt of an electron and te wavelengt of a poton are te same. Te ratio between te energy of tat poton and te momentum of tat electron is ( M) ) ) C ) / 4) /C Ans : e pe C P EP C Pe EP EP C P e
Atomic Pysics. A proton is projected wit a velocity 7 ms at rigt angles to a uniform magnetic field of induction mt. Te time (in seconds) taken by te proton to traverse 9 arc is (Mass of proton.5 x 7 kg and carge of proton. x 9 C) ( 5 M) ).8 x 7 ). x 7 ).4 x 7 4).4 x 7 Ans : If proton is projected rigt angle to te magnetic field it rotating in circular pat te required centripetal force is supplied by force due to magnetic field. Bqv mrω Bqv ω mr mr T π π m Bqv Bq Time taken to transverse 9 arc is 4 T. π T m 7. 4 Bq. Te incident poton involved in te potoelectric effect experiment [5M] ) completely disappears ) comes out wit increased frequency ) comes out wit a decreased frequency 4) comes out wit out cange in frequency Ans : Sol. As te total incident energy is completely absored by te electrons te incident poton completely disappears.. k and k are te maximum kinetic energies of te potoelectrons emitted wen ligt of wave lengt and respectively are incident on a metallic surface. If ten [ 4 M] k k ) k > ) k < ) k k 4) k k Ans : From Einstieins poto electric equation w K. E + X K W W W K W X W Were X X W X K W K X W X W K K Now x>w. Hence K K < <
Atomic Pysics 4. Te de-brogile wavelengt of a particle moving wit a velocity.5 x 8 ms - is equal to te wavelengt of poton. Te ratio of kinetic energy of te particle to te energy of te poton is [ velocity of ligt x 8 ms - ] [ M] ) /8 ) /8 ) 5/8 4) 7/8 Ans : From Compton effect c [ From de-broglie wavelengt] p υ c p υ k p p υ mυ mcp 8 p v.5 8 mc c 8 5. Monocromatic X-rays of wavelengt. A o undergo Compton scattering troug an angle o from a carbon block. Te wavelengt of te scattered X-rays, in A o is take.4 A mc ( M) ). ). ).5 4).8 Ans : ( cosθ).4( cos ) mc +..4 +..A. Te value of de Broglie wavelengt of an electron moving wit a speed of. x 5 ms - is approximately ( M) ) A o ) A o ) A o 4) A o Ans : 4. p mv 9.. m A 5 7. Te maximum wavelengt of ligt tat can be used to produce potoelectric effect on a metal is 5nm. Te maximum K.E of te electrons in joule, emitted from te surface of te metal wen a beam of ligt of wavelengt nm is used: ( M) ) 89. x - ) 9.8 x - ) 8.9 x - 4) 9.8 x - Ans:4 4 Wen is expressed in A ten, W 4 W 4.9eV 5 4 υ.ev K. 4.9.4eV.4. 9 9.84 J 8. Te work function of Potassium is. ev. Wen it is illuminated by ligt of wavelengt A o, potoelectrons are emitted. Te stopping potential of potoelectrons is ( M)
Atomic Pysics ).75 V ).75 V ).5 V 4).75 V Ans : A nm 4 υ.757 ev υ W.757.757eV V.757 V 9. A positron and a proton are accelerated by te same accelerating potential. Ten te ratio of te associated wavelengt of positron and proton will be (M-mass of proton, mmass of positron) ( M) ) M M ) ) m m 4) m m M M Ans: 4 Sol Since bot proton and positron ave te same carge proton mk MeV proton m positron mev M positron 4. In Compton scattering, X-rays of A are scatter from carbon block (Z) and a zinc block (Z) at 9 wit incident beam. Te ratio of scattered wavelengt is ( M) ) : 5 ) 5 : ) : 4) : 5 Ans : Sol Te Compton scattering takes place wen te X-ray is incident on a single electron. It is immaterial weter te electron belongs to te carbon atom or zinc atom te wavelengt of te scattered poton will be identical Ratio of scattered wavelengt : 4. Te work function of metals A and B are in te ratio :. If ligt of frequencies f and f are incident on metal surfaces A and B respectively, te ratio of te maximum kinetic energies of te poto electrons emitted is ( M) ) : ) : ) : 4) :4 Ans: Sol : W: W : v: v : According to poto electric equation, mv W f mv W f ( f ) Ratio of kinetic energies :
Atomic Pysics 4. An x-ray tube is operated at a constant p.d and it is required to get x-rays of wavelengt not less tan. nano-metres. Ten te p.d in kilo-volts is [ M] ) 4.8 ).4 ). 4). Ans : c, V ev e c 4 8. 9 9... v.kv 4