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Note: Please read the Important Instructions and Disclaimer file before solving the MCQs 13. ELECTRONS AND PHOTONS 1) A photon is A) a quantum of light energy B) a quantum of matter C) a positive charged particle D) an instrument for measuring light intensity 2) A photoelectric cell converts A) light energy into heat energy B) light energy into sound energy C) light energy into electric energy D) electric into light energy. 3) The momentum of photon having energy E is A) E/c B) E/c 2 C) E/h D) Zero 4) Einstein’s photoelectric equation is expressed as A) hv = 2 1 W 0 – mv 2 B) hv = W 0 - 2 1 mv 2 C) hv = W 0 + 2 1 mv 2 D) hv = 2 1 mv 2 – W 0 5) Photo-electric effect can be explained only by assuming that light A) is a form of transverse waves B) is a form of longitudinal waves C) can be polarized D) consist of quanta

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  • Note: Please read the Important Instructions and Disclaimer file before solving the MCQs

    13. ELECTRONS AND PHOTONS

    1) A photon is

    A) a quantum of light energy B) a quantum of matter C) a positive charged particle D) an instrument for measuring light intensity

    2) A photoelectric cell converts

    A) light energy into heat energy B) light energy into sound energy C) light energy into electric energy D) electric into light energy.

    3) The momentum of photon having energy E is A) E/c B) E/c2 C) E/h D) Zero

    4) Einsteins photoelectric equation is expressed as

    A) hv = 21 W0 mv2

    B) hv = W0 -21 mv2

    C) hv = W0 +21 mv2

    D) hv = 21 mv2 W0

    5) Photo-electric effect can be explained only by assuming that light

    A) is a form of transverse waves B) is a form of longitudinal waves C) can be polarized D) consist of quanta

  • 6) The energy of a photon corresponding to the visible light of maximum

    wavelength is approximately A) 1 eV B) 1.6 eV C) 3.2 eV D) 7 eV

    7) In order to increase the kinetic energy of ejected photoelectrons, there should be

    an increase in A) intensity of radiation B) wavelength of radiation C) frequency of radiation D) Both the wavelength and intensity of radiation

    8) If h is Plancks constant, the momentum of a photon of wavelength 0.01 is

    A) 10-2 h B) h C) 102 h D) 10 12 h

    9) Plancks constant has the dimensions of

    A) Force B) Energy C) Linear momentum D) Angular momentum.

    10) Number of ejected photoelectrons increases wih increase

    A) in intensity of light B) in wavelength of light C) in frequency of light D) never.

    11) A photon behaves as if it had a mass equal to

    A) hv/c B) hv/c2 C) c2/hv D) hvc.

    12) If the energy of a photon corresponding to a wave length of 6000 is 3.32 10-

    19 joule, the photon energy for a wavelength of 4000 will be A) 1.11 10-19 joule B) 2.22 10-19 joule C) 4.44 10-19 joule

  • D) 4.9810-19 joule

    13) The work function for aluminium surface is 4.2 eV. The cutoff wavelength for the photo electric effect for the surface is A) 1500 B) 2955 C) 3100 D) 2400

    14) The work function of a photoelectric material is 3.32 eV. The threshold frequency

    will be equal to A) 8 1014HZ B) 8 1010HZ C) 5 1020 HZ D) 4 1014HZ

    15) Light of wavelength 4000 is incident on a metal plate whose work function is 2

    eV. The maximum kinetic energy of the emitted photoelectrons would be A) 2.0eV B) 1.5eV C) 1.1eV D) 0.5eV

    16) Given h = 6.6 10-34 joule sec, the momentum of each photon in a given radiation

    is 3.3 10-29kg metre/sec. The frequency of radiation is A) 3 10 Hz B) 6 1010Hz C) 7.5 1012Hz D) 1.5 1013Hz

    17) In a Milikans oil drop apparatus an oil drop of radius 6 10-7m and of density

    0.85 103 kg/m3is seen to fall freely (without any field). The velocity of drop, given viscosity of air to be 1.8310-5 N-s/m2 and neglecting the effect of upthrust force due to air, is A) 30.4510-6m/sec B) 34.6510-5m/sec C) 36.4510-6m/sec D) 36.5410-5m/sec

    18) If the wavelength of light falling on a surface is increased from 3000to 3040,

    then what will be the corresponding change in the stopping potential (given that hc = 12.4 107eV)? A) -5.5 10-12V B) +5.5 10-12V C) -6.7 10-12V

  • D) +6.7 10-12V 19) If the wavelength of light incident on photo-electric cell be reduced from 4000

    to3600,then what will be the change in the cut off potential.(h = 6.6 10-34J s, c = 3.0 108 m/s, e = 1.6 10-19C) A) 0.42Volt B) 0.30Volt C) 0.34Volt D) 0.43Volt

    20) If the voltage across the electrodes of a cathode ray tube is 500 volts then energy gained by the electrons is A) 5 10-17 J B) 1.6 10-19 J C) 1.9 10-27 J D) 8 10-17J

    21) If an electron is accelerated by 8.8 1014m/s2 then electric field required for this

    acceleration is (given specific charge of the electron = 1.76 1011Ckg-1) A) 40 V cm-1 B) 50 V cm-1 C) 60 V cm-1 D) 70 V cm-1

    22) If a beam goes undeflected in Thomsons experiment, then speed of the electron is

    (given E = 30 V cm-1 and B = 6.06 T) A) 2 106 m/s B) 3 106 m/s C) 5 106 m/s D) 3 108 m/s

    23) When an electron enters a magnetic field of 0.01 T with a speed of 107 m s-1 it

    describes a circle of radius 6 mm there. Then specific charge of the electron is given by A) 1.761011C kg -1 B) 1.67 1011Ckg -1 C) 6.711011Ckg-1 D) 1.9 1011Ckg-1

    24) 1.If an electron moving with a speed of 2.5107 m s-1 is deflected by an electric

    field of 1.6 k V m-1 perpendicular to its circular path, then e/m for the electron will be (given radius of circlar path = 2.3 m) A) 1.67 1011C kg -1 B) 1.76 1011C kg -1 C) 1.7 1011C kg-1 D) 1.59 1011Ckg-1

  • 25) If an electron accelerated through a potential difference of 500 volt attains a speed

    of 1.33 107 m s-1 then specific charge of the electron should be A) 1.67 1011 C kg-1 B) 1.7 1011C kg-1 C) 1.62 1011C kg-1 D) 1.76 1011C kg-1

    26) If an electron accelerated from rest through a potential of 200 V acquires a speed

    of 84 1016 m s-1, then its me is

    A) 1.621011 C kg-1 B) 1.661011C.kg-1 C) 1.711011C kg-1 D) 1.761011C kg-1

    27) If a potential of 107 volts is applied across the electrodes of a CRT, then speed

    attained by the electrons is approximately (given:me = 1.76 1011 C/kg)

    A) 1.9 109 m s-1 B) 3 109 m s -1 C) 3 1010 m s-1 D) 3.2 108 m s-1

    28) Energy of a photon of green light of wavelength 5500 is (given: h = 6.62 10-34

    J s-1) approximately A) 2.26 eV B) 2.81ev C) 2.93 eV D) 3.01eV

    29) Wavelength associated with a photon having energy 4.14eV is

    A) 3000 B) 4000 C) 5000 D) 5800

    30) If the work function of a material is 2eV, then minimum frequency of light

    required to emit photo-electrons is A) 3 1010Hz B) 4 1012Hz C) 3.91 1013Hz D) 4.8 1014Hz

  • 31) If the threshold wavelength of radiations required to eject a photoelectron from a metal surface is 6 10-7 m, then work function of the metal is A) 3.3 10-19J B) 1.6 10-19J C) 6.6 10-31J D) 1.9 10-34J

    32) If work function of a metal surface is 3.45 eV ,then maximum wavelength of a

    photon required to eject a photoelectron is A) 3.3 10-7m B) 4.6 10-8m C) 3.6 10-7m D) 7.1 10-9m

    33) Threshold frequency of a photon required to eject a photoelectron from the

    surface of cesium is A) 1.9 1013Hz B) 2.5 1014Hz C) 3 1015Hz D) 4.3 1014Hz

    34) In the graph given below

    if the slope is 4.12 10-15 V- sec, then value of h should be A) 6.6 10-31 J-sec B) 6.6 10-34J-sec C) 9.1 10-31 J-sec D) None of these.

    35) If work function of a metal plate is negligible then the K.E.of the photoelectrons emitted when radiations of 1000 are incident on the metal surface is A) 11.6eV B) 12.4 eV C) 13.6eV D) 14.4 eV

    V0

    Frequency v

  • 36) Maximum velocity of photoelectrons emitted from a metal surface having work

    function 4 eV is (given: frequency of incident radiations is 1015 Hz) A) 2 105 m s-1 B) 2 108 m s-1 C) 3 108 m s-1 D) None of these.

    37) When ultraviolet light of wavelength 1000 is incident on molybdenum, then the maximum velocity of ejected electron (given:work function of molybdenum = 5.0 eV) is A) 2.1106 cm s-1 B) 3.1107cm s-1 C) 1.6108 cm s-1 D) 2.51108cm s-1

    38) If threshold wavelength for tungsten is 2300, then energy of the electrons

    emitted by UV light of wavelength 1800is A) 1.710-11erg B) 2.410-12erg C) 3.110-12 erg D) 4.110-12erg

    39) If maximum velocity with which an electron can be emitted from a photo cell is

    3.75108 cm s-1, then stopping potential is A) 30 volts B) 40 volts C) 50 volts D) 60 volts

    40) Wavelength of light incident on a photo cell is 3000 , if stopping potential is 2.5

    volts, then work function of the cathode of photo cell is A) 1.41 eV B) 1.52 eV C) 1.56 eV D) 1.64 eV

    41) If the frequency of incident light on a certain metal is 8.2 1014 Hz having

    threshold frequency of 3.3 1014 Hz ,then cut off potential is A) 3.0 V B) 4.0 V C) 5.1V D) 2.1V

  • 42) If light of frequency 1015 Hz is incident on sodium having work function 2.5eV,then energy of emitted photoelectrons is A) 1.6 10-19J B) 2.110-19J C) 2.6 10-19J D) 3.0 10-19J

    43) Threshold wavelength for metal is 10,000 . If light of wavelength 5461 is

    incident on it then stopping potential is 1.02 V, then value of Plancks constant is A) 6.45 10-34J-sec B) 6.54 10-34J-sec C) 6.60 10-34J-sec D) 6.67 10-34J-sec

    44) An electron beam is subjected to a magnetic field of 2 10-3 T and an electric

    field of 3.4 104 V m-1 perpendicular to magnetic field. If the deviation of electrons is zero, the velocity of the beam is A) 107 m s-1 B) 1.7107 m s-1 C) 7.1107 m s-1 D) 2.7107m s -1

    45) Uniform electric and magnetic fields are produced pointing in the same direction. An electron is projected pointing in the same direction, then A) the electron turns to right B) the electron turns to left C) the velocity of electron increases D) the velocity of electron decreases.

    46) In Thomsons method for finding specific charge of positive rays, the electric and

    magnetic fields are A) Crossed and separate B) crossed and simultaneous C) Parallel and separate D) parallel and simultaneous

    47) The specific charge for positive rays is much less than that for cathode rays. This

    is because A) they are positively charged B) their charge is very small C) their masses are very large D) experimental approach is defective.

  • 48) The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV fall on it is 4 eV. The stopping potential is A) 2 V B) 4 V C) 6 V D) 10 V

    49) A stream of electrons enters an electric field with 107 m s-1 at right angle to it. If

    the strength of field is 3 104 V/m, the magnetic field acting perpendicular to electric field for producing no deflection of the beam is A) 3 10-3 T B) 0.310-3 T C) 310-4 T D) 310-5 T

    50) A charged drop is balanced in a field of 3 104V/m. If its mass is 9.75 10-12 g, charge on it is A) 3.185 10-18 C B) 3.185 10-20 C C) 3.185 10+18 C D) 31.85 10-18C

    51) A drop of radius one micron carries a charge of 4 electrons. If the density of oil is

    2g/cc, the electric field required to balance it is A) 12.83 V/m B) 12.83 102 V/m C) 12.83 103 V/m. D) 12.83 104V/m

    52) In a Thomsons set up for e/m, the same high tension d.c. supply provides

    potential to anode for acceleration and also the positive voltage to the deflecting plate in the region of crossed fields. If the supply voltage is doubled, by what factor should the magnetic field be increased to keep the electron beam undeflected? A) 2 times B) 2 times

    C) 2

    1 times

    D) 21 times

  • 53) A beam of - particle passes without deflection through crossed electric and magnetic fields with E = 6.6 106N/C and B = 12 N/Am. Their speed is A) 1.8 105 m s-1 B) 5.5 106 m s-1 C) 7.8 106 m s-1 D) 1.1 106 m s-1

    54) In Millikans oil drop method, an oil drop having a charge ne is held stationary

    by applying a potential difference of 400 V between two parallel plates. If the size of the drop is doubled without changing the charge, the potential difference required to keep it stationary is A) 800V B) 1600V C) 3200V D) 200V

    55) For the determination of charge on the oil drop in Millikans method, the radius of

    the oil drop was nearly A) 10-3mm B) 10-5mm C) 10-7 mm D) 10-9mm

    56) Which of the following will not deflect in electric field?

    A) positron B) proton C) neutron D) cathode rays.

    57) In Millikans oil drop experiment an oil drop of radius r and charge Q is held in

    equilibrium between the plates of a charged parallel plate capacitor, when the potential difference is V. To keep a drop of radius 2r,having a charge 2Q in equilibrium between the plates, the potential difference V required is A) V B) 2V C) 4V D) 8V

    58) When a photon of energy 7eV is made incident on a metal then the emitted

    electron is stopped by a stopping potential of -5.5V. The work function of metal will be A) -1.5eV B) 1.5 eV C) 12.5eV D) 37.5eV

  • 59) The work function of a metal is 1.5 eV. Light of wavelength 6600 is made

    incident on it. The maximum kinetic energy of emitted photo-electrons will be A) 1.6 10-19 joule B) 0.6 10-19 joule C) 1.6 10-13 joule D) 1.6 1019 joule

    60) In an experiment of photoelectric emission for incident light of 4000 , the stopping potential is 2V. If the wavelength of incident light is made 3000 , then stopping potential will be A) less than 2 volt B) more than 2 volt C) 2 Volt D) zero

    61) The kinetic energies of the photoelectrons are E1 and E2 with wavelengths of

    incident light 1 and 2 the work function of the metal is

    A) 12

    2211

    EE

    B) 12

    21

    EE

    C) 12

    2121

    EE

    D) 221

    121

    EE

    62) The K.E. of the electron is E when the incident wavelength is . To increase the

    K.E.of the electron to 2E, the incident wavelength must be

    A) hcE

    hc

    B) hcE

    hc

    C) hcE

    h

    D) hcE

    hc

  • 63) Work function of tungsten and sodium are 4.4eV and 2.3 eV respectively. If threshold wavelength of sodium is 5460,then threshold wavelength of tungsten is A) 11360 B) 8000 C) 6000 D) 2840

    64) In photoelectric effect ,the photoelectric current

    A) increases when frequency of incident photons increases B) decreases when frequency of incident photons increases C) does not depend on photon frequency but only on intensity of incident

    beam D) depends both on intensity and frequency of incident beam.

    65) If we consider electrons and photons of the same wavelength ,then they will have

    the same A) velocity B) angular momentum C) energy D) linear momentum

    66) The velocity of the most energetic electrons emitted from a metallic surface is

    doubled when the frequency v of incident radiation is doubled. The work function of this metal is A) zero

    B) 3hv

    C) 2hv

    D) 3

    2hv

    67) Light of wavelength strikes a photo sensitive surface and electrons are ejected

    with kinetic energy E. If the kinetic energy is to be increased to 2E,the wavelength must be changed to , where

    A) = 2

    B) = 2 C) >

    D) 2

    <

  • 68) The maximum velocity of an electron emitted by light of wavelength incident on the surface of a metal of work function is (h = Plancks constant, c = speed of light and m = mass of electron)

    A) 21

    2

    mhc

    B) m

    hc 2

    C) 21

    2

    mhc

    D) 2/12

    m

    hc

    69) The work function of any metal is 4Ev. For emitting photoelectrons of zero

    velocity from the surface of this metal, the wavelength of incident light required must be A) 2700 B) 1700 C) 5900 D) 3100

    70) The curve drawn between velocity and frequency of a photon in vacuum will be a

    A) straight line parallel to frequency axis B) straight line parallel to velocity axis C) straight line passing through origin and making an angle of 450 with

    frequency axis D) hyperbola.

    71) Einsteins work on the photoelectric effect provided support for the equation

    A) E = mc2 B) E = hv

    C) E = 2nRhc

    D) K.E. = 21 mv2

  • 72) In Thomsons experiment, the same H.T. supply provides potential to the anode, as also to positive deflecting plates in the region of crossed fields. If the supply voltage is doubled, then value of the new magnetic field to keep the electron beam undeflected will be

    A) 2B

    B) B2 C) B D) 2B

    73) A stream of electrons enters an electric field normal to the lines of force with a

    velocity of 3 10-7 ms-1. The electric intensity is 1800 V/m. the electron beam is deflected by 2 mm, while traveling through a distance of 10 cm. The e/m in coulomb/kg will be A) 2 1014 B) 2 1011 C) 2 107 D) 2 104

    74) The differences of kinetic energies of photoelectrons emitted from a surface by

    light of wavelength 2500 and 5000 will be A) 1.98 10-19J B) 1.98 10-19 erg C) 3.96 10-19eV D) 3.96 10-19 J

    75) On using light of wavelength 6000 , the stopping potential for a photocell is 2.4

    V. If light of wavelength 4000 is used, then stopping potential will be A) 1.91 V B) 2.81 V C) 3.43 V D) 4.43 V

    76) When a piece of metal is illuminated by mono-chromatic light of wavelength

    then the stopping potential for photoelectric current is 3V0. When the same surface is illuminated by light of wavelength 1.5 , then the stopping potential becomes V0. The value of threshold wavelength for photoelectric emission will be

    A) 34

    B) 2 C) 3 D) 4

  • 77) The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectric emission from the substance is approximately A) 540 nm B) 400nm C) 310 nm D) 220 nm

    78) Wavelength of the radiation of frequency 100 Hz is A) 2 106 m B) 3 106 m C) 4 106 m D) 5 106 m

    79) The unit of Plancks constant is

    A) N m B) eV C) J s-1 D) J s

    80) Plancks constant has the dimensions of

    A) Linear momentum B) Angular momentum C) Energy D) Power

    81) The energy of a photon of light is 3 eV. Then, the wavelength of photon must be

    A) 4125 nm B) 412.5 nm C) 41250 nm D) 4 nm

    82) A photon has velocity c and frequency v. Then, which of the following represents

    its wavelength?

    A) Ehc

    B) chv

    C) 2chv

    D) hv

  • 83) The energy of a photon of wavelength is A) hc B) hc/ C) / hc D) h c/

    84) Which of the following phenomena exhibits particle nature of light?

    A) Interference B) Diffraction C) Polarization D) Photoelectric effect

    85) Photoelectrons are emitted, when

    A) A zinc plate is heated B) A zinc plate is hammered C) A zinc plate is irradiated with ultra violet light D) A zinc plate is subjected to very high pressure

    86) When ultra violet radiation is incident on surface, no photoelectrons are emitted.

    If a second beam causes photoelectrons to be ejected, it may consist of A) radio waves B) infra red rays C) visible light rays D) X-rays

    87) As the intensity of incident light increases

    A) Photoelectric current increases B) Photoelectric current decreases C) Kinetic energy of emitted photo-electrons increases D) Kinetic energy of emitted photo-electrons decreases

    88) Which of the following statements is correct?

    A) The photocurrent increases with increasing frequency B) The photocurrent is proportional to the applied voltage C) The photocurrent increases with intensity of light D) The stopping potential increase with intensity of incident light.

    89) The threshold wavelength of sodium metal is 6780 A.U. The work function of the

    metal will be A) 1.83 eV B) 2.75 eV C) 2.95 eV D) 3.25 eV

  • 90) The photoelectric work function for a metal surface is 4.125 eV. The cut-off wavelength for this surface is : A) 4125 A.U. B) 2062.5 A.U. C) 3000 A.U. D) 6000 A.U.

    91) The strength of photoelectric current depends upon

    A) frequency of incident radiation B) intensity of incident radiation C) angle of incident radiation D) distance between anode and cathode

    92) Consider light of given intensity and frequency falling on a substance that emits

    photoelectrons. The intensity is decreased to one-third its value and the frequency increased by three times. Consequently the velocity of the photoelectrons will A) Remain the same B) Increase or decrease depending on the exact values of the new intensity

    and frequency C) Decrease D) Increase

    93) The kinetic energy (Ek) of a photoelectron varies with the frequency (v) of the

    incident radiation. Which of the following graphs correctly represents this relation?

    94) Photoelectrons are being obtained by irradiating zinc by a radiation of 3100 A.U. In order to increase the kinetic energy of ejected photoelectrons, A) The intensity of radiation should be increased B) The wavelength of radiation should be increased C) The wavelength of radiation should be decreased D) Both wavelength and intensity of radiation should be increased.

  • 95) Photoelectric work function of a metal is 1 eV. Light of wavelength =3000

    A.U. falls on it. The photoelectrons come out with velocity A) 10 m s-1 B) 102ms-1 C) 104 m s-1 D) 106 m s-1

    96) Light of wavelength 5000 A.U. falls on a photo sensitive plate with photoelectric work function of 1.9 eV. The kinetic energy of the photoelectrons emitted will be A) 0.58 eV B) 2.48 eV C) 1.24 eV D) 1.16 eV

    97) Light of two different frequencies, whose photons have energies 1 eV and 2.5

    eV respectively successively illuminate a metal of work function 0.5 eV. The ratio of maximum speeds of the emitted electrons will be A) 1:5 B) 1:4 C) 1:2 D) 1:1

    98) A photo-sensitive material would emit electrons, if excited by photons beyond a

    threshold. To cross the threshold, you would increase A) Intensity of light B) Wavelength of light C) Frequency of light D) The voltage applied to light source

    99) A photon and an electron have the same wavelength. Then, the velocity of photon

    is A) Less than that of the electron B) Greater than that of the electron C) Equal to that of the electron D) None of the above

    100) If we consider electrons and photons of the same wavelength, then they will have

    the same A) Energy B) Velocity C) Linear momentum D) Angular momentum

  • 101) As frequency of incident light is kept constant and intensity of light is increased, the cut- off potential A) Remains constant B) Becomes more negative C) Becomes less negative D) None of the above

    102) Maximum KE and cut off or stopping pot are related with each other as A) Max KE = eVc. B) Max KE = Vc. C) Max KE = Vc/e. D) Max KE = e/Vc

    103) Which of the graphs between Max KE or (cut off pot Vc) and frequency is

    correct?

    A) A B) B C) C D) D

    104) The intercept of the straight line on frequency axis is

    A) Frequency of incident light B) Threshold frequency vo C) Intensity of light D) None of the above

  • 105) A graph between potential V of the anode and photo current I is as shown in the figure. The maximum energy of photo electrons is

    A) 1 eV B) 3 eV C) 2 eV D) 4 eV

    106) Which of the four graphs shown between max KE and intensity light I is correct?

    A) A B) B C) C D) D

  • 107) The graphs between max KE and frequency for two metals X and Y are shown in the adjacent figure. If 1 and 2 are the threshold frequencies, then

    A) 1 = 2 B) 1 < 2 C) 1 > 2 D) 1 and 2 can not be compared

    108) In Thomsons experiment for determining e/m, the potential difference between

    the cathode and the anode (in the accelerating column) is the same as that between the deflecting plates (in the region of crossed fields). If the potential difference is doubled, by what factor should the magnetic field be increased to ensure that the electron beam remains undeflected? A) 2 B) 2 C) 22 D) 4

    109) In Millikans oil drop experiment, a charged oil drop of mass 3.2 10-14 kg is

    held stationary between two parallel plates 6 mm apart by applying a potential difference of 1200 V between them. How many excess electrons does the oil drop carry?

    Take g =10 m-2. A) 7 B) 8 C) 9 D) 10

  • 110) In Millikans oil drop experiment, an oil drop carrying a charge q falls with a terminal velocity 0 when there is no electric field between the plates. An electric field E is applied to keep it stationary. What additional charge should the oil drop acquire so that it begins to move upwards with a velocity 2 0 in the same electric field? A) q B) 2 q C) 3 q D) 4 q

    111) Which one of the following statements is NOT true about photoelectric emission?

    A) For a given emitter illuminated by light of a given frequency, the number of photo- electrons emitted per second is proportional to the intensity of incident light.

    B) For every emitter there is a definite threshold frequency below which no photoelectrons are emitted, no matter what the intensity of light is.

    C) Above the threshold frequency, the maximum kinetic energy of photoelectrons is proportional to the frequency of incident light.

    D) The saturation value of the photoelectric current is independent of the intensity of incident light.

    112) Which one of the following graphs shows the variation of photoelectric current (I)

    with voltage (V) between the electrodes in a photoelectric cell?

  • 113) For a photoelectric cell, the graph showing the variation of the cut-off voltage V0 with frequency (v) of incident light is

    114) The maximum energy Kmax of photoelectrons emitted in a photoelectric cell is

    measured using lights of various frequencies. The graph shows how Kmax varies with v. The slope of this graph is equal to

    A) the charge of an electron B) the charge to mass ratio of an electron C) the work function of the emitter in the cell D) Plancks constant

  • 115) The photoelectric threshold for a certain metal surface is 330 A.U. What is the maximum kinetic energy of photoelectron released, if any, by a radiation of wavelength 1100 A.U.? A) 1 eV B) 2 eV C) 7.5 eV D) no electron is emitted.

    116) When a point source of light is at distance of 50 cm from a photoelectric cell, the

    cut-off voltage is found to be Vo. If the same source is placed at a distance of 1 m from the cell, the cut-off voltage will be A) V 0 /4 B) V 0 /2 C) V 0 D) 2 V 0

    117) The photoelectric current in a photoelectric cell depends upon

    A) the nature of the metal used as a emitter B) the wavelength of the incident light C) the intensity of the incident light D) all the above parameters

    118) No photoelectrons are emitted from a metal if the wavelength of light exceeds

    6000 A.U. The work function of the metal is approximately equal to A) 3 10 16 J B) 3 10 19 J C) 3 10 20 J D) 3 10 22 J

    119) The threshold wavelength for photoelectric emission from a material is 5200 A.U.

    Photoelectrons will be emitted when this material is illuminated with monochromatic radiation from a

    A) 50-watt infrared lamp B) 100-watt red neon lamp C) 40-watt sodium lamp D) 5-watt ultraviolet lamp

  • 120) Light of Wavelength 3500 A.U. is incident on two metals A and B whose work functions are 4.2 eV and 1.9 eV respectively. Which metal will emit photoelectrons? A) A B) B C) Both A and B D) Neither A or B

    121) When monochromatic light falls on a photosensitive material, the number of

    photoelectrons emitted per second is n and their maximum kinetic energy is K max . If the intensity of the incident light is doubled, then A) both n and K max are doubled B) both n and K max are halved C) n is doubled but K max remains the same D) K max is doubled but n remains same

    122) When ultraviolet light is incident on a photocell, its stopping potential is V0 and

    the maximum kinetic energy of the photoelectrons is K max . When X rays are incident on the same cell, then. A) V0 and K max both increase B) V0 and K max both decrease C) V0 increases but K max remains the same D) K max increases but V0 remains the same

    123) The work function for aluminum surface is 4.2 e V and that for sodium surface is 2.0 e V. The two metals were illuminated with appropriate radiations so as to cause photo emission. Then A) both aluminum and sodium will have the same threshold frequency. B) the threshold frequency of aluminum will be more than that of sodium. C) the threshold frequency of aluminum will be less than that of sodium. D) the threshold wavelength of aluminum will be more than that of sodium.

    124) X-rays of frequency v are used to irradiate sodium and copper surfaces in two

    separate experiments and the stopping potentials determined. Then A) the stopping potential is more for copper than for sodium. B) the stopping potential is more for sodium than for copper C) the stopping potential is the same for sodium and copper D) the stopping potential for both will vary as 1/v.

  • 125) The photoelectric emission from the surface of a metal starts only when the light incident on the surface has a certain A) minimum frequency B) minimum wavelength C) minimum intensity D) minimum speed.

    126) At frequencies of the incident radiation above the threshold frequency, the

    photoelectric current in photoelectric cell increases with increase in A) intensity of incident radiation B) wavelength of incident radiation C) frequency of incident of radiation D) speed of incident radiation

    127) The photoelectrons emitted from a metal surface

    A) are all at rest B) have the same kinectic energy C) have the same momentum D) have speed varying from zero up to a certain maximum value.

    128) The wavelength in air associated with a photon of energy E is (c is the speed of

    light in air and h is the Plancks constant)

    A) Ehc

    B) cEh

    C) hEc

    D) hcE 129) A metal whose work function is 3.3 eV is illuminated by light of wave length 3

    10 7 m. What is the threshold frequency for photoelectric emission ? Plancks constant =6.6 10 34 Js

    A) 0.4 1015 H Z B) 0.8 1015 H Z C) 1.6 1015 H Z D) 3.2 1015 H Z

    130) In Q.129, the maximum energy of photoelectrons is

    A) 0.825 e V B) 1.0 e V C) 1.225 e V D) 1.5 e V

  • 131) In Q 129, what is the stopping potential ? A) 0.825 V B) 1.0 V C) 1.225 V D) 1.5 V

    132) Violet light can cause photoelectric emission from a metal but blue light cannot. If

    sodium light is incident on the metal, then A) the photoelectric current decreases B) the number of photoelectrons ejected per second increases. C) the velocity of photoelectrons increases D) no photoelectric emission occurs.

    133) What is the stopping potential for photoelectrons ejected from a photosensitive

    material of work function 1.6 eV when it is irradiated by photons of energy 2.4 eV? A) 0.8 V B) 2.0 V C) 4.0 V D) none of these

    134) When a certain photosensitive surface is illuminated with monochromatic light of

    wavelength , the stopping potential for photoelectric current is 2V 0 . When the same surface is illuminated with monochromatic light of wavelength 2 , the stopping potential is V 0 /2. The threshold wavelength for photoelectric emission is A) 1.5 B) 2.0 C) 2.5 D) 3

    135) The threshold frequency for a certain photosensitive metal is v 0 . When

    illuminated by light of frequency v = 2v 0 , the stopping potential for photoelectric current is V 0 . What will be the stopping potential when the same metal is illuminated by light of frequency v =3 v 0 ? A) 1.5 V 0 B) 2 V 0 C) 2.5 V 0 D) 3 V 0

  • 136) The threshold frequency for a certain photosensitive metal is v 0 . When it is illuminated by light of frequency v = 2 v 0 , the maximum velocity of photoelectrons is V 0 . What will be the maximum velocity of the photoelectrons when the same metal is illuminated by light of frequency v =5 v 0 ? A) 2 V 0 B) 2 V 0 C) 2 2 V 0 D) V 0

    137) The threshold wavelength for a metal whose work function is W 0 is 0. What is

    the threshold wavelength for a metal whose work function is W 0 /2?

    A) 4

    B) 2

    C) 2 0 D) 4 0

    138) When the accelerating voltage applied on the electrons, in an X-ray tube, is

    increased beyond a critical value A) the spectrum of white radiation is unaffected B) only the intensities of various wavelengths are increased C) only the wavelength of characteristic radiation is affected D) the intensities of characteristic lines relative to the white spectrum are increased but there is no change in their wavelength.

    139) The work function of substance is 4.0eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately A) 540nm B) 400nm C) 310nm D) 220nm

  • 140) Two photons of energies twice and thrice the work function of a metal are incident on the metal surface. Then the ratio of maximum velocities of the photoelectrons emitted in the two cases respectively, is A) 2 :1 B) 3 : 3 C) 2:3 D) 1 : 2

  • 13. ELECTRONS AND PHOTONS

    Ques. No. Answer 1 A 2 C 3 A 4 C 5 D 6 B 7 C 8 D 9 D

    10 A 11 B 12 D 13 B 14 A 15 C 16 D 17 C 18 A 19 C 20 D 21 B 22 C 23 B 24 C 25 D 26 D 27 A 28 A 29 B 30 D 31 A 32 C 33 D 34 B 35 B 36 A 37 C 38 B 39 B 40 D 41 A 42 C 43 B 44 B 45 D

    Ques. No. Answer 46 C 47 C 48 B 49 A 50 A 51 D 52 B 53 B 54 C 55 A 56 C 57 C 58 B 59 B 60 B 61 A 62 B 63 D 64 C 65 B 66 D 67 D 68 C 69 D 70 A 71 B 72 B 73 B 74 D 75 C 76 B 77 C 78 B 79 D 80 B 81 B 82 A 83 B 84 D 85 C 86 D 87 A 88 C 89 A 90 C

  • Ques. No. Answer 91 B 92 D 93 D 94 C 95 D 96 A 97 C 98 C 99 B 100 C 101 A 102 A 103 C 104 B 105 D 106 D 107 B 108 A 109 D 110 B 111 D 112 A 113 D 114 D 115 D

    Ques. No. Answer 116 C 117 D 118 B 119 D 120 B 121 C 122 A 123 B 124 B 125 A 126 A 127 D 128 A 129 B 130 A 131 A 132 D 133 A 134 D 135 B 136 B 137 C 138 D 139 C 140 D