CET II PUC: PHYSICS: ATOMIC PHYSICS INTRODUCTION TO ATOMIC PHYSICS, PHOTOELECTRIC EFFECT DUAL NATURE OF MATTER, BOHR S ATOM MODEL SCATTERING OF LIGHT and LASERS QUESTIONS ) Wic of te following statements are correct? a) Electromagnetic waves can ave wavelengts of several kilometres. b) Hig energy gamma rays travel at a iger speed tan lower energy ones in free space. c) X-rays are transverse waves. d) An electromagnetic wave can penetrate matter. ) (a), (b) and (c) 2)(b), (c) and (d) 3) (a), (c) and (d) 4)(a), (b) and (d) 2) Given tat te mass of neutron or proton is approximately 840 times te mass of electron, ten te ratio of specific carge of electron to tat of α-particle is ) 840 2)3680 3) 4) 840 3680 3) Of te following te grap wic represents te variation of Energy (E) of te poton wit te wavelengt (λ) is E E E E λ λ λ λ ) 2) 3) 4) 4) Matc te following: List List 2 a) Burning candle i) Line absorption spectrum b) Sodium vapour lamp ii) Continuous emission spectrum c) Sun iii) Band emission spectrum d) Bunsen flame iv) Line emission spectrum ) a iii, b i, c iv, d ii 2) a iv, b ii, c i, d iii 3) a ii, b iii, c i, d iv 4) a ii, b iv, c i, d iii 5) Te kinetic energy of te potoelectron increases by 0.5 ev wen te wavelengt of incident ligt is canged from 500nm to anoter wavelengt wic is nearly ) 400 nm 2) 700 nm 3)000 nm 4) 250 nm
6) Ligt potons of energies ev and 2.5 ev are successively incident on a metal surface of work function 0.5 ev, ten te ratio maximum velocities of te emitted electrons will be ) : 5 2) : 4 3) : 3 4) : 2 7) Wen UV ligt of wavelengt 00 nm is incident on silver surface of work function 4.7eV, a negative potential of 7.7V is required to stop te potoelectrons from reacing te collector plate. Te potential wic is required to stop te potoelectrons wen ligt of wavelengt 200nm is incident on it will be ).5V 2) 3V 3)4.5V 4) 6V 8) Wen a monocromatic point source of ligt is at a distance of.50 m from a potoelectric cell, te cut-off voltage and te saturation current are respectively 2V and 20 µa. If te same source is placed 75cm away from te potoelectric cell, ten ) Te stopping potential will be 2V and saturation current will be 80 µa 2) Te stopping potential will be 4V andsaturation current will be 80 µa 3) Te stopping potential will be 2V and saturation current will be 40 µa 4) Te stopping potential will be 4V andsaturation current will be 40 µa 9) If E is te energy, de-broglie wavelengt is proportional to ) E for bot potons and particles 2) E for potons and E /2 particles 3) E /2 for bot potons and particles 4) E /2 for potons and E for particles 0) Te resolving power of an electron microscope at 0 kv is R. Te potential increased to 90 kv. Te new resolving power will be ) R 2) 3R 3) R/3 4) 9R ) For given kinetic energy wic of te following as te smallest de-broglie wavelengt? ) Electron 2)Proton 3)Neutron 4) alpa particle 2) Te ionization energy of electron in te ydrogen in its ground state is 3.6 ev. Te atoms are excited to iger energy levels to emit radiations of 6 wavelengts. Maximum wavelengt of emitted radiation corresponds to te transition between ) n = 2 to n = 2)n = 3 to n = 3)n = 3 to n = 2 4) n = 4 to n =3 3) Hydrogen atom emits blue ligt wen an electron jumps from n = 4 to n = 2 energy level. Te colour of ligt emitted by te atom wen te electron jumps from n = 5 to n = 2 energy level is ) red 2) yellow 3) green 4) violet 4) Force acting on an electron in a Bor orbit wit principal quantum number n is proportional to ) n 2)n 2 3) n 4 4) /n 4 5) Te kinetic energy of te orbiting electron in te ydrogen atom is E, ten te potential energy and te total energy wit proper sign are respectively ) E, 2E 2) 2E, E 3) E, 2E 4) 2E, E 6) Te orbital radius of te electron in te ydrogen atom canges from r to 4r, ten te energy of te orbital electron cange from E to ) E/4 2) E/2 3) 2E 4) 4E 7) Wen ydrogen atom is excited state, emits a poton of energy 2. ev wen it makes a transition to a ground state, its orbital angular momentum canges by ).05 0 34 Js 2)2. 0 34 Js 3) 3.6 0 34 Js 4)4.22 0 34 Js
8) How many times does te electron go around te first Bor orbit in one second? 2 2 4 π mr ) 2) 3) 4) 2 π mr 2 2 4 π mr 2 π mr 9) Angular momentum of an electron in an orbit of H atom is proportional to ) r 2) 3) r 4) r r 20) Energy levels A, B, C of a certain atom correspond to increasing values of energy i.e.,e A < E B < E C. If λ, λ 2, λ 3 are te wavelengts of radiations corresponding to te transitions C to B, B to A and C to A respectively, wic of te following statements is correct? λ λ2 )λ 3 = λ + λ 2 2) λ = 3)λ + λ 2 + λ 3 = 0 4) λ 2 2 2 3 = λ + λ2 λ + λ 3 2 2) If λ, λ and λ 2 are te wavelengts of stokes lines, incident ligt and anti-stokes lines respectively ten ) λ = λ = λ 2 2)λ <λ<λ 2 3)λ >λ>λ 2 4) λ <λ 2 <λ 22) Ceck te incorrect statements on scattering of ligt. ) Blue colour of sky is due to Rayleig scattering 2) In Rayleig scattering intensity of scattered ligt is proportional to /λ 4 3) Clouds aving droplets of water, wic scatter all te wavelengts almost equal, so tey are generally wite. 4) Te sun looks reddis at sunset and sunrise due to Tyndall scattering. 23) A composite beam of ligt containing wavelengts 440nm and 550nm is passed troug a gas, in a given direction, te ratio of te intensity of scattered ligt of tose wavelengts will be ) 6 : 25 2) 25 : 6 3)256 : 625 4) 625 : 256 24) Consider te statements. A laser beam (a) is igly monocromatic (b) as angular divergence (c) is an electromagnetic wave (d) cannot be used in optical communication. ) (a) (b) and (c) are correct 2) (a) (c) and (d) are correct 3) (a) and (c) are incorrect 4) (b) and (d) are incorrect 25) Wic of te following statement is WRONG wit respect to Ruby laser? )It is developed by T. Maiman. 2)Te wavelengt of ligt emitted by it is 694.3nm. 3) It is a continuous laser. 4) It is a tree level laser. 26) Te tecnique to measure large distances using lasers is known as ) LIDAR 2) RADAR 3) SONAR 4) bot (2) and (3) 27) Ligt of wavelengt 300nm is incident on a surface of area 4 cm 2. If te intensity of ligt is 50mW/m 2, ten rate at wic potons strike te target (per second) is ) 7 0 5 2)9 0 3 3)3 0 0 4) 6 0 9 28) An X ray poton as a wavelengt of 0.02 Å. Its momentum is ) 3.3 0 22 kg m/s 2) 6.6 0 2 kg m/s 3) 6.6 0 24 kg m/s 4).65 0 22 kg m/s 29) Wic one is te correct about te electromagnetic waves in free space? ) Electric and magnetic fields ave a pase difference of π/2. 2) Te speed of te wave is c = B/E.
3) Energy distribution of electric and magnetic fields are unequal. 4) Electromagnetic waves transport bot energy and momentum. 30) Te maximum velocity of potoelectrons emitted by a poto emitter is 7 0 5 m/s. If te specific carge of an electron is.75 0 C/kg, stopping potential of te emitter is ) 0.7 V 2).4 V 3)2.8 V 4) 3.5 V 3) If te velocity of a particle is reduced to one-tird ten te percentage increase in its de-broglie wavelengt is ) 50% 2) 00% 3) 200% 4) 300% 32) A proton and an α-particle are accelerated troug te same p.d.. Te ratio of teir de-broglie wavelengts is ) 2) 2 3) 8 4)/ 8 33) Energy required for te electron excitation in Li ++ from first orbit to tird orbit is ) 2. ev 2)36.3 ev 3)08.8 ev 4) 22.4 ev 34) Pick out te wrong statement from te following: ) As observed in spectrograps of ig resolving power te H α, H β and H γ lines are not single lines 2) According to Sommerfeld, te pat of an electron around te nucleus is an ellipse 3) Te speed of te electron moving in an elliptical orbit is a constant 4) Te principal quantum number n takes integral values from to 35) Rayleig scattering law is not applicable to ) Water molecules 2)Gas molecules 3) Particles very small compared to wavelengt of ligt 4) large dust particles 36) Te material used in Ruby lasers is ) Naturally occurring Ruby 2) Amorpous Al 2 O 3 3) Crystalline Al 2 O 3 doped wit cromium 4) Cromium crystal doped witaluminium 37) Coose te WRONG statement out of te following. ) X rays are used in of study of crystal structure. 2) Like visible ligt, X rays are diffracted at anobstacle. 3) X rays can cause ionization of te atoms of a gases. 4) X rays are deflected by electric and magnetic fields. 38) Wic of te following is not correct regarding te poton? )ν = E/ 2) Momentum of poton = /λ 3) Mass of poton = /cλ 4) λ = ν/c 39) If potons of wavelengt 60nm are incident on ydrogen, ten te maximum kinetic energy of emitted electrons will be ) 3 ev 2) 5 ev 3)7eV 4) 9 ev 40) Te work function of a surface of a potosensitive material is 6.2eV. Te wavelengt of te incident radiation for wic te stopping potential is 5V lies in te ) Infra-red 2) Visible ligt 3)Ultraviolet ligt 4) X-ray 4) Te kinetic energies of potoelectrons emitted from a metal are K and K 2 wen it is irradiated wit ligts of wavelengt λ and λ 2 respectively. Te work function of te metal is Kλ K 2λ2 Kλ+ K2λ2 Kλ2 K2λ Kλ2 + K2λ ) 2) 3) 4) λ λ λ + λ λ λ λ + λ 2 2 2 2
42) In Sommerfeld s atomic model corresponding to principal quantum number n = 3, tere will be ) 3 circular orbits 2) 3 elliptical orbits 3) circular and 2 elliptical orbits 4) 2 circular and elliptical orbits 43) Consider te spectral line resulting in te transition from n = 2 to n =, in atoms / ions given below. Te igest frequency radiation is emitted by ) Hydrogen atom 2)Deuterium atom 3)Singly ionized elium 4) Doubly ionized litium 44) In wic of te following systems will te radius of te first orbit (n = ) be minimum? ) Hydrogen atom 2)Deuterium atom 3)Singly ionized elium 4) Doubly ionized litium 45) Te wavelengt of te matter waves is independent of ) mass 2)velocity 3)momentum 4) carge 46) A poton of energy 9 ev is incident on a surface wose tresold frequency is.6 0 5 Hz. Te kinetic energy of te emitted electrons is ) 2.37 ev 2)7.4 ev 3)9 ev 4) 0.6 ev 47) Te momentum of a neutron of de-broglie wavelengt 0. nm is ) 6.6 0-24 kg ms - 2)6.6 0-4 kg ms - 3)6.6 0-34 kg ms - 4) 6.6 0-4 kg ms - Additional Questions: INTRODUCTION TO ATOMIC PHYSICS ) Infrared rays are used in long distance potograpy because ) Tey travel wit te velocity of ligt in vacuum. 2) Tey can be easily produced. 3) Due to teir long wavelengt, scattering is low. 4) Due to teir small wavelengt, scattering is ig. 2) An electromagnetic radiation as energy of 3.2keV. Ten te radiation belongs to te region of ) Infra-red 2) Visible ligt 3)Ultraviolet ligt 4) X-ray 3) Flas spectrum tat occurs at a total solar eclipse is ) Line absorption spectrum 2)Line emission spectrum 3)Band emission spectrum 4)Band absorption spectrum 4) Band spectrum is obtained wenever te incandescent vapour of te excited substance is in ) Atomic state 2)Molecular state 3)Ionised state 4)Atomicor Molecular state 5) A radio transmitter radiates 0.kW power at a wavelengt 98.6 nm. Te number of potons emitted per second by it is ) 0 0 2)0 20 3)0 30 4)0 40 6) Consider te following statements about electromagnetic waves and coose te correct ones. A) EM waves aving wavelengt 000 times smaller tan visible ligt waves are called X-rays. B) Ultraviolet waves are used sterilization of water and surgical equipment s.
C) de-broglie waves are electromagnetic in nature. D) Electromagnetic wavesexibit polarization wile sound waves do not. ) (A), (B) and (C) 2)(A), (B) and (D)3) (B), (C) and (D) 4)(A), (C) and (D) 7) Te ratio of specific carge of te electron and nucleus of ydrogen atom is nearly ) 2) 2 3) 4 4) 836 8) Identify te correct arrangement of electromagnetic radiations in ascending order of frequency. )γ- rays, X- rays, Visible ligt, radio waves. 2) Ultraviolet rays, visible ligt, X-rays, Infra-red rays. 3) Radio waves, micro waves, visible ligt, UV rays. 4) Infra-red rays, UV rays, γ- rays, X- rays. 9) In determining specific carge of electrons by Dunnington, electrons are made to negotiate a circular pat by ) Electric field only 3) Bot electric and magnetic fields in te same directions 2) Magnetic field only 4) Mutually perpendicular electric and magnetic fields PHOTOELECTRIC EFFECT ) Potons wit energies twice and ten times te work function of a metal are incident successively on a metal. Te ratio of te maximum energies of te potoelectrons emitted in te two cases is respectively ) : 5 2)5 : 3) : 3 4) : 9 2) Work function for copper is 4.4 ev. Te potential difference tat must be applied to stop te fastest electrons released wen ligt of wavelengt 00 nm is incident is ) 4 V 2)8 V 3)6 V 4)20 V 3) On plotting frequency of incident radiation along X axis and stopping potential along Y axis, a straigt line is obtained. Its slope is ) /e 2)e/ 3) 4)/ 4) For a potoelectric cell, te grap in Fig. sowing te variation of te cut-off voltage V 0 wit frequency (v) of incident ligt is V 0 V 0 V 0 V 0 0 0 ν ν 0 ν 0 ν ) 2) 3) 4) 5) A potosensitive metal is incident wit radiations of wavelengt 400 nm and ten wit radiations of wavelengt 800 nm. Wat will be te difference in te maximum energy of te potoelectrons ) 0.5 ev 2) ev 3).5 ev 4) 2 ev
6) Monocromatic ligt of frequency ν irradiates a potocell and te stopping potential is found to be V. Wat is te new stopping potential of te cell if it is irradiated by monocromatic ligt of frequency ν 2? ) V + ( ν2 ν) 2) V ( ν2 ν) 3) V + ( ν+ ν2) 4) V ( ν+ ν2) e e e e 7) Wen radiation of wavelengtλ is incident on a metallic surface, te stopping potential is 4.8V. If te same surface is illuminated wit radiation of double te wavelengt, ten te stopping potential becomes.6 V. Ten te tresold wavelengt for te surface is ) 2λ 2) 4λ 3)6λ 4) 8λ DUAL NATURE OF MATTER ) If te kinetic energy of a particle is reduced to one-fourt ten te percentage increase in te de-broglie wavelengt is ) 4% 2)00% 3)44% 4) 200% 2) If E, E 2 and E 3 are te respective kinetic energies of an electron, an alpa particle and a proton eac aving te same de-broglie wavelengt ten ) E > E 3 > E 2 2)E 2 > E 3 > E 3)E > E 2 > E 3 4)E = E 2 = E 3 3) Wavelengt of a γ- ray poton wose energy is alf te rest mass energy of an electron is ) 5 0 2 m 2)5 0 8 m 3)7 0 2 m 4)7 0 2 m 4) A marble of mass 30g is moving wit a speed of 80 kmp. Te de-broglie wavelengt associated wit is nearly ) 0 m 2)0 0 m 3)4 0 34 Å 4)4 0 24 Å 5) Coose te only correct statement out of te following. ) only a carged particle in motion is accompanied by matter waves 2) only subatomic particles in motion are accompanied by matter waves 3) any particle in motion, weter carged or uncarged, is accompanied by matter waves 4) no particle, weter at rest or in motion, is ever accompanied by matter waves 6) Te de-broglie wavelengt associated wit an electron wen it is accelerated troug a p.d. of 40 kv is ) 0.64 pm 2)6.4 pm 3)6.4 Å 4) 0.064 pm 7) Te de-broglie wavelengt of a particle moving wit velocity 0 8 m/s is equal to te wavelengt of a poton. Te ratio of kinetic energy of te particle to te energy of te poton is ) /8 2) /6 3)¼ 4) ½ 8) Electrons used in an electron microscope are accelerated by a voltage of 25kV. If te voltage is increased to 00kV ten te de-broglie wavelengt associated wit te electrons would ) increases to 2 times 2) increases to 4 times3)decreases by 2 times4)decreases by 4 times
9) Electrons beave like waves in G.P. Tomson experiment because tey ) Ionize te gas 2) Are affected by electric field 3) Are deflected by magnetic field 4) Diffracted by a crystal 0) Wave nature of matter is revealed by ) Potoelectric effect 2) Raman effect 3) Electron diffraction 4) Compton effect ) Te de-broglie wavelengt of electron is 0.5nm, te retarding potential to stop it is ) 2V 2) 3V 3)4V 4) 6V 2) Te momentum of electron aving de-broglie wavelengt00å is ) 6.6 0 32 g cm/s 2) 6.6 0 25 g cm/s 3)6.6 0 2 g cm/s 4) 6.6 0 29 g cm/s 3) Electron microscope works on te principle of ) Particle nature of electron 2) Wave nature of electron 3) Wave nature of ligt 4) Quantum nature of ligt BOHR S ATOM MODEL ) Te ratio of kinetic energy of te n = 2 state electron for te ydrogen atom to tat of He + ion is ) 2) 2 3)½ 4) ¼ 2) An electron in a ydrogen atom as moved from n = to n = 5 orbit, ten ) Bot potential energy and kinetic energyof te system increases. 2)Bot potential energy and kinetic energy of te system decreases. 3)Potential energy of te system decreases and kinetic energy of te system increases. 4) Potential energy of te system increases and kinetic energy of te system decreases. 3) In case of ydrogen atom te ratio of energy difference between second orbit and tird orbit to te energy difference between te first orbit and te second orbit is ) 9/4 2)4/9 3)5/27 4) 27/5 4) Te minimum required to strip off energy of 0 times ionized sodium atom (Z = ) of its last electron is ) 3.6eV 2)3.6 ev 3) 3.6 2 ev 4)(3.6/) ev 5) Te de-broglie wavelengt of te electron in te first excited state of te ydrogen atom is nearly ) 0.53Å 2).67 Å 3)3.33 Å 4) 6.66 Å 6) Te transition of te electron from n = 4 to n =3 in a ydrogen like atom results in UV radiation. Infra-red radiation will be obtained in te transition ) n = 2 to n = 2)n = 3 to n =2 3)n = 4 to n =2 4) n = 5 to n =4
7) Te ionization potential of ydrogen atom is 3.6 V. Hydrogen atoms in te ground state are excited by electromagnetic radiation of energy 2.75eV. How many spectral lines will be emitted by te ydrogen atom? ) 2) 2 3)3 4) 6 8) Fine structure of spectral lines is accounted in Sommerfield atom model by considering ) Elliptical orbits around te nucleus 2) Spin of electron 3)Relativistic cange in mass of electron in elliptical orbits 4) Space quantisation of orbits 9) Te area of te electron orbit for te ground state of H-atom is A. Te area wen it is in te first excited state is ) 2A 2)4A 3)8A 4) 6A 0) Te ionization potential of ydrogen atom is 3.6V. Te energy needed to be supplied to ionize ydrogen atom in te first excited state. ) 3.6 ev 2)3.4 ev 3)6.8 ev 4) 27.2 ev ) An electron jumps from first excited state to ground state of ydrogen atom, ten te percentage cange in speed of electron ) 25% 2) 50% 3) 00% 4) 200% 2) An electron jumps from te 4 t orbit to 2 nd orbit of ydrogen atom.givente Rydberg s constant R = 0 5 cm -, te frequency (in Hz) of emitted radiation will be ) 3 0 5 6 2) 3 0 5 6 3) 9 0 5 6 4) 3 0 5 4 SCATTERING OF LIGHT ) Raman effect is explained on te basis of ) Corpuscular teory of ligt 2) Waveteory of ligt 3) Electromagnetic teory of ligt 4) Quantum teory of ligt. 2) Pick out te incorrect statement from te following ) Stokes lines ave wavelengts greater tan tat of te incident ligt 2) Stokes lines are more intense tan te anti-stokes lines 3) Te intensity of stokes lines is found to depend on temperature 4) Stokes and anti-stokes lines are polarized. 3) Te blue colour of te sky is due to te fact tat ) Red ligt is absorbed 2) Blue ligt is preferentially absorbed 3) Blue ligt is preferentially scattered 4) Blue is te natural colour of te sky 4) In a given direction, te intensities of scattered ligt substance for two beams of ligt are in te ratio 8: 6. Te ratio of frequency of te first beam to te frequency of te second beam is ) 3:2 2) 2:3 3) 9:4 4)4:9
LASERS ) Average life time of metastable state is ) 0 3 s 2)0 8 s 3)0 4 s 4) 0 20 s 2) Te output of Ruby Laser is pulsed because )Ruby rod gets eated. 2) Stimulated emission is delayed. 3) Optical pumping cannot be continuous. 4) Stimulated emission occurs faster tan population inversion. 3) Te red colour of Ruby laser ligt is due to electron transition between energy levels of ) Aluminium 2)Oxygen 3) Cromium 4) All of tese 4) Te most relevant property involved in te cutting of metals by a laser beam is ) Monocromaticity 2) Coerence 3)Directionality 4) Sarp focus 5) Ifr a = rate of absorption, r b = rate of spontaneous emission and r c = rate of stimulated emission, ten for Laser action te condition to be satisfied is ) r b >r a 2)r c >r a 3)r c >r b 4) bot (2) and (3) 6) Potonics is concerned wit ) Lasers 2) Fibre optics 3) Optical computing 4) All tese 7) In Ruby laser stimulated emission is due to transition from ) One excited state to lower excited state 2) metastable state to a certain lower state 3) metastable to an excited state 4) metastable state to ground state only 8) Ruby laser belongs to te class of ) Solid state lasers 2) Gas lasers 3) Liquid lasers 4) Semiconductor diode laser