-
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