Modern Physics Part 2

7/29/2019 Modern Physics Part 2

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QUESTTON BANKONLY ONE OPTION IS GORREGT

\

I(A) 'L /l --t) |

l"o 9lo (c) lo?'orn" t=qu" no tne intensitv of a beam of lisht f"l!!9 "-i t1"-:'.,1':: :l?:?i""?'?:fl1,1"t"titt are increasedil: ffi; "t *". i*"iiil ;#"i";.y "r pLrnrXorcerroi oe eration :T:ltiill#:#:;ilfi'l3:i:::llx";:1"' ',1'X#:ffi;ifti ff,tl:l':fl::::::il:"ll3l"3lXil"Ji,1'ixli[A] il$::::,'ffi;'#ffi'*]i..'"i',lLilis] [,,n. o,,.,re s,su,.,,J,,r.nd would increase the

photoelectric current

current bY a factor of two.Lisht comins from a disctrarserub: nr!,"-d,yil1.1vli,?9:ll"^'5^","-[Ti:**::lTJ'otoerectric cerlLrgnt comlng rro-I1l a urDv,rrarYvjs::'^',:-,^';^i;;r;Y; nno nf tha followino values

A point source of ligth is used in a photoelectric emetal, the stoPPing Potential :(A) will increase 1t^lYlli*-:::?::remain constant (D) willeither increase or decrease'

(D) 1IVb{I

factor of two'ncreasethemaximumkineticenergyofthephotoe|ectronsbyafactorofgreaterthantwoandwi||haveffect on the magnitude of photoelectric current produced'(D) not produce any effect on the kinetic ;.*gt;iih" emitted electrons but will increase the photoelectric'(

I-Ts

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14. A point source causes photoelectric effect from a small metal plate. Which of the following curves mayrepresent the saturation photocurrent as a function of the distance between the source and the metal ?

(c)by a light of wavelength 1., and K,

(D) K1> 2K2

(A)hfl

(A) Arithmetic Progression;lffiar mon ic Prog ression

Let K., be the maximum kinetic energy of photoelectrons emittedcorresponding to l"r. lf 1.., = 2fr, then :(A)2K.' = K, (B) K.' = 2Q K"K,. iIn a photoelectric experiment, the potential ditference V that must be maintainedbetween the illuminated surface and the collector so as justto prevent any elecironfrom reaching the collector is determined for different frequencies f of the incidentillumination. The graptl obtained is shown.The maximum kinetic energy of the electrons emitted at frequency f.' is

(fl _ fo) (D) eV.,(f.,-fo)

(B)2 : 1 (C) 1 :aCut off potentials for a metal in photoelectric etfect for light of wavelength 1",, 1", and 1., is found to be V.,, V,and V. volts if V., V, and V. are in Arithmetic Progression and 1,,', 1., and 1". will be:(B) Geometric Progression

(D) NonePhotons with energy 5 eV are incident on a cathode C , on a photoelectric cell. The maximum energy of theemitted p eV. When photons of energy 6 eV are incident on C, no photoelecreagh the ping potential of A relative to C issQ{gv -3v (c)-1v (D)4vIn a photoelectric experiment, the collector plate is at 2.0V with respect to the emitter plate made of coppera = 4.sev). The emitter is illuminated by a source of monochromatic light of wavelength 200nm.(Afthe minimum kinetic energy of the photoelectr!,6)the maximum kinetic energy of the photoelectif the polarity of the battery is reversed then an

if the polarity of the battery is reversed then anBy increasing the intensity of incident light keeping frequency 1v > v6) Trxeo on rne surTace oT meral(A) kinetic energy of the photoelectrons increases

Radiation of two photon energies twice and five times the work function oi metal are incident sucessively on themetal surface. The ratio of the maximum veloci$ of photoelectrons emitted is the two cases will be(D)a:1

' (D) no effectIn a photoelectric experiment, electrons are ejected from metals X and Y by light of intensity I and frequencyf. The potential difference V required to stop the electrons is measured for various frequencies. lf Y has agreaterwork function than X ; which one of the following graphs best illustrates the expected results?

umber of emitted elections increases- inetic energy and numberof electrons increases

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(c) The photoelectric currentwill remain the same.(u) None oTlnese I \

I

I

toheavyparticleis K3t*1 _3q' -rr -.^. - ,^, 3q(B) 4eoh (c) ,%t (D) +on

-l r 1 e (B) )'- a ' (G) l.^ * J2 (D) none of theseJn*In ,&. (B)l,.atInotnJn * In , &. (B) 1,. a t (G) l'n cc J' (D) none oTmeseIn dn 3hThe angular momentum of an electron in the hydrogen atom is fn.tlere h is Planck's constant' The kineticenergy of this electron is:(A'l 4 53 eV 1.51 eV (C) 3'a eV (D) 6'8 eV(A)a.ffiev 1.51 eV (G)3'4ev (uro'

d with shortest and longbst wavelengths wouldbe emitted from the atom by the transitions-labelled:(A) D and C respectively -T.]m^. " ='(B)CandAresPectivelY)CandDlesPectivelY r- '\-' n=2(D)Aand C respectivelY _ n= 1

ln hydrogen and hydrogen like atoms, the ratio of difference of energies Eon-Ern and Ern-En varies with itsln hYdrogen and hYdrogenatomic number z and n as: (C)zlnA) z2 ln2 (B) r'tnaIn a hydrogen atom, the electron is in nth excited state. lt may come down to second excited state byan atiffaranr rerarralannfhq What is the value of n: tf n -\ 1 fg ten differentwavelengths. What is the value of n:(B) 7 (c) I Cn-t) q

2Enlnh (B)2Enn/hlf the electron in a hYdrogen nrequired to ionise the atom? n(A) 6.54 x 1O-1e (B)

it's (n-1)th Bohr's radius. the value(A) 1 (B) 2 (c) 3An electron in hydrogen atom after absorbing energy photons._can jump between energy states n1 andn"(no > n,). Then it may return to ground state afteremitting six differentwavelengths in emission spectrum'ii? jr"rlv or"rittJ dnotons is e-itherequalto, less than orgreaterthan the absorbed photons. Then nl and(A)nr=4,n1=3 (B)[2=5'ot=3 z=4Thee|ectroninahydrogenatommakestransitionfromMshcentripetal acceleration of the electron is(A)9:4 (B)sl:16 (C)a:9

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The radius of Bohr's first orbit is ao. The electron in nlOrUit has a radius:(A) nao (B) aotn - lPfn'?ao (D)aJn2m is 13.6 volt. The energy required to ron from the(C) 13.6 eV (D

by an identically charged particle muo times thatofelectron. Now the radius of K shellwill be

Hydrogen atoms absorb the light and subsequently emit radiations of ten different wavelengths. The value ofl" is 103 nm (C) 73 nm (D) 88 nmWhenahydrogenatom,initiallyatrestemits,aphotonresultingintransitionn=5-+n=l,itsrecoilspeedis about(A) 10a m/s (B) 2 x 1f2 m/s .2 m/s (D) 3.8 x 10-2 m/sAn electron collides with a fixed hydrogen atom in its ground state. Hydrogen atom gets excited and thecolliding electron lose all its kinetic energy. Consequenty tre hydrogen atom may emit a photon conesponding

40.

to the largest wavelength of the Balmer series. The min. K.E.of colliding electron will be

42. -,=

(D).)"bo-

(B) 3wbo-

\ 'a{t

Consider the spectral line resulting from the transition n = 2 -+ n = 1 in the atoms and ions given below. Theshortestwavelength is produced by: :(A) hydrogen atom (B deuterium atom(C) singly ionized helium oubly ionized lithium

The total energy of a hydrogen atom in its ground state is -13.6eV. lf the potential energy in the first excited

(A)1:4 (B)4:1 (D)8:The electron in hydrogen atom in a sample i tate, then the numberof different spectrum linesobtained in its emission spectrum witlbe:1 + 2 + 3 + ..........+(n - 1)1 + 2 + 3 + ....................+ ( n )1 + 2 + 3 + ..........+(n + 1)(D)1x2x3x x(n-l)

staBonary nyn is less thann is less thanwhen initialk than 13.6eV.

(D) perfectly inelastic collision cannot take place., The electron in a hydrogen atom make a transition from an excited state to the ground state. Which of thefollowing statement is true?Its kinetic energy increases and its potentialand totalenergies decreaseIts kinetic energy decreases, potential energy increases and its total energy remains the same.(C) lts kinetic and toalenergies decrease and its potentialefergy increases.(D) its kinetic potential and total energies decreases.

state is taken as zero then the total energy in state will be :(A)-3-4eV (B) 3.4 eV 8eV (D) 6.8eVstationary hy----^- -1^- :- ---"-r ^t-'^

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V/' The magnitude of angular momentum, orbit radius and frequency of revolution of electron in hydrogen atomcorresponding to quantum number n are L, r and f respectively. Then according to Boh/s theory of hydrogenfrl is constant folallslqjlxfrl2 is constant for all orbits

atom,(A) fr2l is constant for all orbits(C) PrL is constant for all orbits

oo6od

The "Ko" X-rays emission line of tungsten occlevels in this atom is about

8 MeV and that for C13 is 7'5 MeV' The energy required to(C) 9.5 MeV (D) 9'34 MeV

ndE,respective|y.TwoatomsofXfusetogiveoneatomofY(C) Q= 2E,,+E, (D) Q= 2E2+E1

Radius of the second Bohr obit of singty ionised helium atom ts

n electron in Bohr's hydrogen abm has an energy of -3.4 eV. The angular momentum of the electon is(B)h t2n(D)2hltlf each fission in a U235 nucleus releases 200 MeV how many fissions must occurs per second to produce

hlnnh | 2rc ( n is an integer)

a power of 1 l(A/(A) 1.325 x 1013 (C) 1.235 x 1013 (D) 2.135 x 1013 \69.\

' Th. rest mass of the deuteron , f H , .is equivalent to an energy of 1976 MeV the rest mass of a proton isequivalent to g3g MeV and that of a neutron to g40 MeV. A deuteron may disintegrate to a proton and aneutron if it :

is48MeVandQ-va|ueofthereactionis50MeV.Thema.ssat daughter nucleus is in ground state)(C) 104 (D) none of theseln the uranium radioactive series the initialnucleus is rrU238, and the final nucleus is rrPb206'.When theuranium nucleus decays to lead, the number of o - pi'rtictes emitted is.. and the number of p-particlesemitted'..(A) 6, 8 1/(d) a, o (c)16' 6 (D) 32'12The radioactive sources A and B of half lives of 2hr and 4 hr respectively, initially contain the same number^a ti^i^taara+i^^ 6ra in tha refin 'of radioactive atoms. At the end of 2 hours, their rates of disintegration are in the ratio :

.125 x 1013

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isa

the

1(A) 1- -e 1(B) c I(D) 1- cIn a RA element the fraction of initiated amount remaining after its mean life time is

40o/ool a radioactive sample is left undecayed aftertime t has elapsed. What percentage of the initialsamplewilldecay in a totaltime 2t :(A)20To t -Wtr* (QaOTo (D)38%

t2(A) t(B)1:2 (c) e

Ao(A) 'F

relates m, and mr?(A)mv=tr*1

An(D\ n

72.

= Al e(tr-t2)/T

R2Activity of a radioactive substance is R, at time t, and R, at time t2(t2 t t1) Then the ratio * is:

(B) .-i.(q+tr;,,'Therc are two radionuclei A and B. A is an alpha emitter and B is a beta emitter. Their distintegrationconstants are in the ratio of 1 : 2. What should be the ratio of number of atoms of two at time t = 0 so thatprobabilities of getting a and B particles are same at time t = 0. (D) e-'

,.,"[T)

,r'fhe activity of a sample reduces from Ao to Ao / ^f in one hour. The activity after 3 hours more will beAo(c) tF68. Half life of radium is 1620 years. How many radium nuclei decay in 5 hours in 5 gm radium? ( Atomic weightof radium =223)(A)9.1 x 1012 (B)3.23 x 1015 (C) 1.72 x 1020 (D) 3.3 x 101769. , Half life for certain radioactive element is 5 min. Four nuclei of that element are observed at a certain instant\ z of time.Afterfive minutesAssertion (A) : lt can be definitely said that two nucleiwill be left undecayed.Reasoning (R) : After half life i.e. 5 minutes, half of total nucleiwilldisintegrate. So onlytwo nucleiwill be leftundecayed. Then(A) A is correct & R is conect explanation of A.(B) Both are correct. But R is not conect explanation of A.s incorrect & R is correct.

th are incorrect.. A certain radioactive nuclide of mass number m, disintegrates, with the emission of an electron and yradiation only, to give second nuclied of mass r umber m' Which one of the following equation correctly(B)mv=mx-2 (G)mv=mx-1 ffiY=ffi*

The number of a and p- emitted during the radioactive decay chain starting from 33unu and ending atrt3uPt i.(A) 3o & 60- (B) ac & 5p- \96cr a +g- (D) 6cr & 6p-The activi$ of a sample of radioactive material is A, at time t., and A, at time t, (! t t,). lts mean life is T.(A) A,t, = Ar! At -Az(B) t, _ tl = constant

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tion i of a radioactive sample decays in one mean life, and a fraction f, decays in one half-life',fz(B) f1< f2(c)[=f,(D) trjtaybe (A), (B) or (C) depending on the values of the mean life and half lifeA radioactive substance is being produced at a constant rate of 10 nuclei/s. The decay constant of thesubstance is 1/2 sec-1. Afterwhattime the number of radioactive nucleiwill become 10? Initiallythere are nonuclei present. Assume decay law holds forthe sample. C , N"

1(B) los (2) sec l!B(1s86sec (o) ^i; secvity of a sample is R, at time T,, and R, at

have disintegrated in time (T2 -Tl) is prol(A) (RlTl - R2T2) 1 - R2) T (c)(Rr -R2)/Tay constant of the end product of a radioactive series is(B) infinite (C) finite (non zero) (D) depends on the end product

I t. r +\(c) *lNrlle-^r'+Nzl2 "-nr') (D) + N,,1., Nrl,re-(lr+lz)tlmagine a Young's double slit interferen wit with bst movif,g eectronsproduced from an electron gun. Thedi ive se maximum if -(A) the accelerating voltage in the electron gun is decreased

(D)the distance between the slits is decreased.lf radiation of allwavelengths from ultraviolet to infraabsorption lines will be observed in the :(A) Lyman series (B) Balmer series, oth (A) and (B) (D) neither (A) nor (B)

(D) E = 6.8 eV i. = 6.6 x 10-11 m

be brought to almost rest by this atom. = q.\ " fwhen electron of kinetic energy 125eY

Aal

\i,(E

(D)(Rr- )(Tr )Nr- \- ,-Ril'T77. At time t = 0, N., nuclei of decay constant l.i & N2the mixture is :

(A) N,Nre{i"'+r'')t

nuclei of decay constant 1", are mixed. The decay rate of i

(B) +

79.-

ONE OR MORE THAN ONE OPTION MAY BE CORREGTh question.ntialdepends on

(B) intensi$ of the incident light by varies source distancemitte/s properties (D) frequency and intensity of the incident light

An electron in hydrogen atom first jumps from second excited state to first excited state and then, from firstexcited state to ground state. Let the ratio of wavelength, momeqtup anct energy of photons in the tivo casesbe x, y and z, then select the wrong answer/(s) :

of the electron is E and its de-Broglie wavelength is 1,, thenlf the kinelt =- ltd(A) E = 6.8 eV l. = 6.6 x 10-10 m

(C) E = 3.4 eV tr. = 6.6 x 10-11 m

*' t7s 3;Yrt "d"1L, then \^ = h'\E= 3.4 eV l, = 6.$ x lQ-ro t '' f ";arn

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f

A beam of ultraviolet light of all wavelengths passes through hydrogen gas at room temperature, in thex-direction. Assume that all photons emitted due to electron transition inside the gas emerge in the y4irection.Let A and B denote the lights emerging from the gas in the x and y directions respectively.

ome of the incident wavelengths will be absent in A.(B) Only those wavelengths will be present in B which are absent in A.

ee, i e level of potential energy is assumed to be zero at the ground state

level. Choose the incorrect statement.ase in the value of nse in the value of n.mains the same..6 eV.

The speed of electron in the first Bohr orbit of deThe wavelength of flrst Balmer line of deuterium

(D) The angular momentum of electron in the first Bohr orbit of deuterium is more than that of hydroEen. , I $;-'lFnAn be the area enclosed by the nu orbit in a hydwill pass through originwill be a stright line will sloPe 4

(C) will be a monotonically increasing nonlinear curv(D) will be a circle.A neutron collkje headon with a stationary hydrogenare correct (Assume that the hydrogen atom and neutron has same mass) :

lf kinetic energy of the neutron is less lhan20.4 eV collision must be elastic.lf kinetic energy of the neutron is less than 20.4 eV coliision may be inelastic.Inelastic collision may be take place only when initial kinetic energy of neutron is greater than 20.4 eV.Perfectly inelastic collision can not take place.n a nucleus with atomic number Z and mass numberA undergoes a radioactive decay process:oth Z and A will decrease, if the process is cr decaywill decrease but A will not change, if the process is pt decay

(C) Z will decrease but A will not change, if the process is p- decayZ and Awill remain unchanged, if the process is 1 decay.

(A) electrons accelerate through a potentialdifference of 12.75 kV in the Ooolidge tubelectrons accelerate through a potential difference of 18.75 kV in the Coolidge tube

(C) de-Broglie wavelength of the electrons reaching the anticathode is of the order of 1 Opm ^ o(D) de-Broglie wavelength of the electrons reaching the anticathode is 0.01A. \ Hoten1al difference applied to an X-ray tube is increased. As a result, in the emitted radiation:

-:-.,- ...^..^ t^--tL i-^-^^^^^e intensity increases (B) the minimum wave length increases(C)the intensity decreases he minimum wave length decreasesg'

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eus increasesconstant = 1ses and laterdecreases

itia||ybindingenergypernucleonincreasesand|aterdecreasese binding energy per nucleon increases when the neufon-proton ratio increases'

ot a lf;Canucleus. Then(A) M, = 2M. (B) M2 > 2Ml s/t '|IBIM, ' 2s.' ,,


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ANSIilER I{EYEXER.CISE.II1. 885 2. (a) 2.25eV, (b) 4.2eV (c) 2.0 eV 0.5 eV 3. (a) 0.6 volt, (b) 2.0 rnA4. when the potential is steady, photo electric emission just stop when hu = (3 + 1)eV = 4.0 eV

the

the(ii),be

5.76 x 10-11A487.06 nm

LtLz7u, +)r,

(i) 5, 16.5 eV,- h/eEt2

6. 15/8V.9.

13.

5 10207' G' 8or, 8' 2 eV 6.53 x 10aJ-s

22.8 nm16. 5

10. 4.26m1s,13.2eV 11. 7:36 12.14. 18(5R) 15. 1.257 x 10-23Am2

17.'!9.z'3-

23.

36.4 A, 340 eV20.24.

26.

- 680 eV54.4 eV

offr

h2n 1.06 x 10-11 m27. n=3,3:1----- flAt + *,eo + v (ii) 4.2 x

23. =33.298 uW

18. z=3,n=722. 23.6 MeV1ff yearsTtrz = 10.8 sec)

Ilns)t= l*f he ehB(i) 4nm (ii) Snrn1.4.5.

4.8 x 1016, 4.0 cm 2.Ideutron = Ineutron = 8'6 Pml.-11.24 eV

(a) 105 si ; (b) 286.18; (d) 111 sKE = 151 eV dr.u< = 0.5 A

8/3 x 1018sec 27. 2.48x19-tz^ 28.EXERCTSE-III

1.99eV. 0.760V 3. 1.1 x 1012

3.1 x 106 m/s 7. (i) 2 ; (ii)23.04x 10-1sJ ; (iii) 4 -+ 1, 4 +3489.6 eV 25.28 A,.

11.13.

16.

20.

21.22.

9. 6.8 eV 5 x 1015 Hz 10.(i) 1.875 x 10aV $)2.7 x 10-15J, (iii) 0.737A, (iv) 2.67 x 1frlsJ 12. 6.04 x 10eyrs4.87 MeV 14. 3.3 x 10-6 g 15. 1.7 x 1010 years5196 yrs 17. v = ul.t o.2es[at-*A-r-^')l19. 61= L ^ JmS(i)Allowedvaluesof energyof neutron=6.36eVand0.312eV;Allowedvaluesof energyof Heatom =17.84eV and 16.328 eV fii) 18.23 x 1014 Hz, g.MO x 101s Hz ,11.6 x 101s Hz

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.r; Itlt'EXEREISE-IV1. (a)c, (b)A2. (a) n = 2,2= 4;GS.E. -217.6 eV Min. eneQy = 10.58 eV; (b) 6.25 x 101e per sec, 0, 5 eV3.A4.8

z= 42

to. (a) C; (b) B ; (c) B; (d) E; (e) C 11.14. C

I:10-5 Wm2

13. A-er'|),6,e5.*,# |hl ;r\J/21. J, 22. n = 1.546 x 1018 Hz

26, n=2429. B 30. Ba3. B 34. B,D 35. C'O. A 41. B16.(A) + P, Q, S, T ; (B) -+ a; (C) + S: (D) -+ S51. B 52. C Sl. D

5. 3,4052.3 nm

{6. A20. A25. A,C

6. 5 x 107,200$uc,23eVI8FA

4Vl\/9..Vp12. C

27. (A) P, O; (B) P, R; (C) S, P; (D) P, Q, R 28. A31. (A) R, P; (B) Q, S; (C) P; (D) a 32. A36. C 37. A 38. A 39. A42.D43.D4.A45.847. A '18. 1 49. 7 50. C

18. C23. B

1. A,C5, A,C,D8. A,B12. A, D16. A, D

15. A19. A24. C

6.A7.D13.C11D20. B 21. B27.C?8.A34. D 35. B41. C 42. C48. A 49. B55. B 56. A62. C 63. B69. D 70. D76.An.C

1.C8.A15. C_22. A29. C36. C/|3. D'57.864. C71. C78. B

2.89.416. C23. B30. D37. A4.C51. C58. D65. D72. C79. A

QI'ESTIONS BANKONLY ONE OPTION IS GOR,REGT3.C4.D5-Cl0.B11.C1LD17. A 18. c 19. B24.A25.A?f83r. A 32. D 3l. C38.A39.A$.C45. B /16. C 17. A52.8s3.A5+B59. B 60. B 61. C66. A 67. B 68. B73. A 74. C 75. B

IIi

I

1..- ONE OR MORE THAN ONE OPTIOX IAY BE CORRECT2.86.89. A,C13. A, C3.87. A,B10. A, B, D14. C, D

1. A,C,D11. B15. A, C

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Modern Physics Part 2

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