Electrons & Protons

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Very important physics notes...


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


    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


    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


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