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Particle Nature Of Light Mcq
Quiz 5
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Q.1
If E1, E2 and E3 are the respective kinetic energies of an electron, an alpha particle and a proton each having the same de Brogli wavelength then
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a)E1 > E3 > E2
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b) E2 > E3 > E1
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c)E1 > E2 > E2
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d)E1=E2=E3
Explanation
When wavelength is same then E ∝ /√m Answer: (b)
Q.2
A particle of mass 10-31 kg is moving with velocity equal to 105 m/sec. The wavelength of the particle is equal to
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a) 0
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b) 6.6 ×10-8 m
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c)0.66 m
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d)1.5 × 107
Explanation
Use formula λ=h/p=h/mvAnswer: (b)
Q.3
An electron has a speed of 100 m/s with an accuracy of 0.005%. The uncertainty in position will be
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a) 0.14 m
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b) 1.4 m
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c)0.014 m
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d)14.0 m
Explanation
Accuracy=0.005 the uncertainty for velocity of 100 m/s=0.005 m/s Answer:(a)
Q.4
A proton when accelerated through a potential difference of V volts has a wavelength λ associated with it. An α-particle in order to have the same λ must be accelerated through a potential difference of
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a) V volt
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b) 4V volt
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c) 2V volt
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d) V/8 volt
Explanation
Answer: (d)
Q.5
The momentum of photon ( in kgms-1) of frequency 109 cycles per second is
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a)7.3 ×10-29
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b) 2.2 × 10-33
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c)6.6 ×10-26
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d)3.1
Explanation
p=E/cbut E=hν p=hν/c substitute the value and solveAnswer: (b)
Q.6
An electron accelerated through a potential difference of V volts has wavelength λ associated with it. Mass of proton is nearly 2000 times that of electron. In order to have the same λ for proton, it must accelerate through a potential difference o
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a) V volts
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b) 2000 V volt
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c)V/20000 volt
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d)√(2000) v volt
Explanation
Answer: (c)
Q.7
A tiny particle of mass 10-13 kg moving with a velocity of 10 cm/sec is associated with the wavelength
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a) 6.62 × 10-20 m
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b)6.62 × 10-20 cm
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c)6.62 × 10-34 cm
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d)6.62 × 10-13 m
Explanation
Use formula λ=h/p Answer:(a)
Q.8
The momentum of electrons having a wavelength of 100 A.U. is
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a) 6.6 ×10-32 gm ×cm / sec
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b) 6.6 ×10-29 gm ×cm / sec
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c) 6.6 ×10-25 gm ×cm / sec
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d) 6.6 ×10-21 gm ×cm / sec
Explanation
λ=h/p Answer: (d)
Q.9
In Bohr's atom the number of de Broglie waves associated with an electron moving in nth permitted orbit is
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a)n
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b) 2n
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c)n/2
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d)n2
Explanation
From Bohr postulate mvr=nh/2π mv=nh/2πr - - - eq(1) Now λ=h/mv - - - eq(2) From eq(1) and eq(2) we get λ=(2πr/n) ∴ 2πr=nλ ∴ circumference=nλ ∴ n waves are permitted in nth orbitAnswer: (a)
Q.10
A moving particle is associated with a wave packet or group of waves. The group velocity is equal to
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a) velocity of light
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b) velocity of sound
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c)velocity of particle
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d)1/ particle velocity
Explanation
Answer: (c)
Q.11
According to wave mechanics, a material particle is associated with
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a) a single wave
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b) a wave packet
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c)two progressive waves
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d)a ripple
Explanation
Answer:(b)
Q.12
The de Broglie wavelength of an electron in 1.224 Å. The energy of electron is eV is
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a) 1 eV
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b) 10eV
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c) 100eV
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d) 1224eV
Explanation
Answer: (c)
Q.13
The de Broglie wave length associated with an electron moving with (1/10)th of the velocity of light is
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a)0.24 ×10-19 m
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b) 0.24 ×10-10 m
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c)1.24 ×10-10 m
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d)0.48 ×10-10 m
Explanation
mass of electron from formula From the equation for wavelength Answer: (b)
Q.14
The uncertainty principle is applicable to
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a) Large system only
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b) small system only
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c)sub atomic particles only
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d)both sub-atomic and large particle
Explanation
Answer: (d)
Q.15
The de-Broglie wavelength of a molecule of thermal energy KT ( K is Boltzmann constant and T is absolute temperature) is
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a)
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b)
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c)
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d)
Explanation
from the formula Answer:(b)
Q.16
The de-Broglie wavelength associated with thermal neutron ( t=51°C say) is of the order of the
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a) Distance between the atoms in the crystal
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b) size of the nucleus
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c) Bohr's radius
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d) size of grain
Explanation
Which is equal to inter atomic spacing Answer: (a)
Q.17
An electron, proton and a car all have same wavelength. The one possessing highest velocity is
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a)electron
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b) proton
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c)car
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d)all have same velocity
Explanation
Answer: (a)
Q.18
The de Broglie wavelength of 150 eV electron will be
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a) 1 Å
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b) 12.27 Å
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c)0.5 Å
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d)1.5 Å
Explanation
electron have energy 150 eV it means electron is accelerated by 150 VFrom formula λ=√(150/V)Å λ=√(150/150)=1 ÅAnswer: (a)
Q.19
In the hydrogen atom an electron is moving in nth orbit. The circumference s of the orbit and the de Broglie wavelength, λ of the moving electron are related by the equation
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a) s=nλ
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b) s=n/λ
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c)s=λ/n
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d)s=1/ nλ
Explanation
From Bohr postulate mvr=nh/2πmv=nh/2mπNow λ=h/mv=h×(2π/nh)∴ 2πr=nλ∴ circumference S=λn Answer:(a)
Q.20
The uncertainty in the location of a particle is equal to its de Broglie wavelength then the uncertainty in its velocity will be
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a) Its velocity
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b) Half of its velocity
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c) Twice its velocity
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d) Four times its velocity
Explanation
Δx Δp=h ∴ Δx mΔV=h given Δx=λ=∴ ΔV=h/ mλ but h/λ=mV ∴ ΔV=V Answer: (a)
Q.21
What is the de Broglie wave length of an electron accelerated through 40kV?
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a)614 pm
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b) 61.4 pm
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c)6.14 pm
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d)0.614 pm
Explanation
Use formula λ=√(150/V)ÅAnswer: (c)
Q.22
The de-Broglie wavelength associated with moving electrons is 0.24×10-10 m. The voltage applied between grids to bring it to rest is
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a) 1000 volts
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b) 2597 volts
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c)2597 volts
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d)none of above
Explanation
Energy of grids must be equal to kinetic energy of electronAnswer: (b)
Q.23
Matter waves are similar in nature to
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a) X-rays
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b) γ-rays
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c)Cathode rays
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d)none of the above
Explanation
Answer:(d)
Q.24
The propagation constant of the de Broglie waves associated with an electron is
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a) Proportional to its mass
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b) Proportional to its momentum
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c) Proportional to its energy
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d) Inversely proportional to its energy
Explanation
Answer: (b)
Q.25
The wavelength of the matter wave is independent of
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a)mass
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b) velocity
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c)momentum
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d)charge
Explanation
Answer: (d)
Q.26
An electron accelerated by a potential difference of V volt posses a de Broglie wave length λ. If the accelerating potential is increased by a factor of 4, the de-Broglie wavelength of the electron will be
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a) Remains unchaged
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b) Becomes 4 times
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c)Becomes Half
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d)Becomes double
Explanation
Use formula λ=√(150/V)ÅAnswer: (c)
Q.27
A photon and electron have same wave length then
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a) photon has greater momentum
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b) electron has greater momentum
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c)they have the same momentum
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d)none of the above
Explanation
λ=h/p Answer:(c)
Q.28
The function of the crystal in Davisson and Germer experiment is
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a) To reflect the electron beam
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b) To refract the electron beam
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c) To diffract the electron beam
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d) To focus the electron beam
Explanation
Answer: (c)
Q.29
The interplanar spacing of crystal is 1.225 Å. the maximum order of diffraction of electrons accelerated through a potential difference of 10 kV is
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a) 1
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b) 20
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c)100
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d)1000
Explanation
Answer:(b)
Q.30
A particle of mass 1kg is moving with a velocity of 1m/s. The de-broglie wavelength associated with it will be
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a) h
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b) h/2
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c) h/4
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d) 2h
Explanation
Answer: (a)
0 h : 0 m : 1 s
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