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Physics NEET MCQ
Atom And Nucleus Mcq
Quiz 3
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Q.1
two radioactive substabce A and B have decay constant5λ and λ respectively. At t=0 they have same number of nuclei. the ratio of number of nuclei of A to those of B will be (1/e)2 after time interval .. [ CBSE-PMT 2007]
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a) 1/4λ
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b) 2λ
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c) 1/2λ
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d) λ / 4
Explanation
given λA=5λ and λB=λ At time t=0 (No) A=(No) B Accoring to radioactive decay From (1) and (2) Answer: (c)
Q.2
Which one of the following is stable ? [ AFMC 1997]
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a) positron
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b) proton
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c)electron
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d)neutron
Explanation
Answer: (b)
Q.3
Intensity of X-rays depends upon the number of ----- . [ AFMC 2000]
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a) positron
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b) neutrons
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c)protons
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d)electrons
Explanation
To produced X-ray electrons are bombarded on the target. Larger the number of electrons bombarded greater will be intensity of X-rays.Answer: (d)
Q.4
Which of the following statement is not correct ? [ AFMC 1999]
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a)Infra-red photons have more energy than photons of visible light
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b)Infra-red rays are invisiable but can cast shadows like visiable light
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c)Photographic plates are sensitive to ultraviolet rays
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d) Photographic plates are sensitive to infra-red rays.
Explanation
Infrared photons have frequency less than red light so its energy will be less than visible light. Answer:(a)
Q.5
Bohr`s theroy was modified by ------- . [ AFMC 2003]
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a) Rutherford and Soddy
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b) Planck
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c) Hund
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d) Sommerfield
Explanation
Bohr`s theory was modified by Planck who gave quantum mechanical approach to structure of atom. Answer: (b)
Q.6
)Atoms having different atomic number as well as different mass number but having same number of neutrons. --- [AFMC 2003]
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a)isotopes
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b) isobars
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c)isotones
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d)isodiaphers
Explanation
Atoms having different atomic numbers and mass numbers but same number of neutrons are called isotones.Answer: (c)
Q.7
) The intensive property among the following is [ AFMC 2003]
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a) energy
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b) volume
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c)entropy
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d)temperature
Explanation
Intensive property is the property which is not dependent upon mass or matter. Temperature is the intensive property.Answer: (d)
Q.8
) the total energy of electron is 3.555 MeV. If its potential energy is zero, then its kinetic energy is ---- . [ AFMC 2000}
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a)3.555 MeV
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b) 3.5 MeV
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c)3.545 MeV
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d)3.045 Mev
Explanation
Total energy=K.E. + P.E. 3.555 MeV=K.E. + 0 K.E.=3.555 MEV Answer:(a)
Q.9
) The ratio of dimensions of Plank`s constant and that of the moment of interia is the dimension of ---- . [ AFMC 2007]
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a) frenqucy
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b) velocity
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c) angular momentum
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d) time
Explanation
Planck`s constant, Answer: (a)
Q.10
) Kinetic energy of an electron accelerated in a potential difference of 100 V is{AFMC 1999}
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a)
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b) 1.6 ×10 -29 J
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c)1.6 × 1021 J
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d)1.6 × 10-17 J
Explanation
Answer: (d)
Q.11
) Photoelectric effect shows{AFMC 2003}
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a) wave nature of electrons
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b) particle nature of light
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c) both (a) and ( b)
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d)none of the above
Explanation
Photoelectic effect shows particle nature of light. Answer: (b)
Q.12
) What is the ratio of the shortest wavelength of the Balmer series to the shortest wave length of the Lyman serises?{AFMC 2011}
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a)4 : 1
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b) 4 : 3
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c)4 : 9
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d)5 : 9
Explanation
For Lyman series Answer:(a)
Q.13
) Fraction of tritium left after 150 years ( half life of tritium is 12.5 years) is{AFMC 2011}
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a) 1 / 1024
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b) 1 / 2048
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c) 1 / 4096
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d) 1 / 8192
Explanation
n=150 / 12.5=12 Answer: (c)
Q.14
In the nuclear reaction , there is conservation of{AFMC 2000}
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a)momentum
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b) mass
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c)energy
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d)all of these
Explanation
Ln a nuclear reaction there is conservation of mass, momentum, and energy. So option (d) is correct.Answer: (d)
Q.15
) Rutherford's alpha particle experiment show that the atoms have{AFMC 2011}
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a) electron
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b) neutrons
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c) nucleus
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d) proton
Explanation
Rutherford's experiment disclosed that atoms are mostly hollow and in the centre there is a small sized nucleus. Thus it discoved the position of nucleus.Answer: (c)
Q.16
3) The velocity of an electron in the inner most orbit of an atom will be{AFMC 2002}
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a)highest
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b) lowest
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c)mean
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d)zero
Explanation
We know that from Bohr's theorem of atomic structure So, when radius is small velocity will be large. Hence , velocity of electron in the inner most orbit will be highest.Answer: (a)
Q.17
4) Which of the following is most unstable ?{AFMC 2005}
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a) Electron
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b) Proton
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c)Neutron
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d)alpha - particle
Explanation
Neutron has a mean life time of 886 seconds and it decays to an electron and antineutrino. Hence, neutron is an unstable particle. Answer: (c)
Q.18
5) The strength of the transverse magnetic field required to bend all photoelectrons within a circle of radius 50 cm when light of wavelength 4000A is incident on barium emitter is ( work function of barium is 2.5eV){AFMC 2004}
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a) 5.2× 10 -6 T
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b) 4 × 10 -4 T
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c)4.0 × 10 -6 T
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d)5.2× 10 -4 T
Explanation
Energy of emitted photoelectrons Answer:(a)
Q.19
6) After 2 hrs, 1/16 th of intial amount of certain radioactive isotope remains undecayd. The half life time of isotope is{AFMC 2005}
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a) 15 min
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b) 30 min
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c) 45 min
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d) 60 min
Explanation
Answer: (b)
Q.20
7) If the energy of a hydrogen atom in nth orbit is En. then energy in nth orbit of a singly ionized helium atom will be{AFMC 2007}
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a)4 En
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b) En/4
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c)2 En
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d) En/2
Explanation
Energy of helium atom in nth orbit=En Mass of the singly ionsed helium atom is 4 times as that of hydrogen atom. ∴: Energy of singly ionised helium atom=4 EnAnswer: (a)
Q.21
8) What is not released in nuclear disintegration?{AFMC 2009}
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a) Electrons
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b) Protons
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c)Helium nucleus
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d)gama rays
Explanation
Electrons do not reside in the nucleus but they revolve round it in different orbits. So, they can't release during nuclear disintegration. A helium nuclease, protons and gamma rays can be released by the nuclei of radioactive elements. Answer: (a)
Q.22
9) When light of wavelength 300nm falls on a photoelectic emitter, photoelectrons are liberated. For another emitter, light of wavelength 600nm is sufficient for liberating photoelectrons. The ratio of the work function of the two emitters is{AFMC 2008}+
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a) 1 : 2
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b) 2 : 1
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c)4 : 1
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d) 1 : 4
Explanation
Answer:(b)
Q.23
) Photoelectric effect shows{AFMC 2003}
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a) wave nature of electron
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b) particle nature of light
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c) both (a) and (b)
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d) none of these
Explanation
Photoelectric effect shows particle nature of light.Answer: (b)
Q.24
) Hard X-rays for the study of fractures in bones should have a minimum wavelength of 10-11 m. The accelrating voltage for electrons in X-ray machin should be{AFMC 2006}
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a)< 124 kV
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b) > 124 kV
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c)between 60 kV and 70 kV
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d)=100 kV
Explanation
X-ray of wavelength less than 10 A are called hard X-rays.as minimum wavelength is Hence, the accelerating voltage for electrons in X-ray machine should be less than 124 kV.Answer: (a)
Q.25
) Alpha particles are [ AFMC 2003]
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a) ionised helium atom
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b) hydrogen atom
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c)neutral atom
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d)all of these
Explanation
Alpha particles has two unit positive charge and 4 unit of mass and ionised helium atom also have 2 units charge and 4 unit of mass. Answer: (a)
Q.26
) Half lives of two radioactive substances A and B are respectively 20 min and 40 min. Intially, the samples of A and B have equal number of nuclei. After 80 min the ratio of remaining number of A and B nuclei is [ AFMC 2006]
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a) 1 : 16
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b) 4 : 1
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c)1 : 4
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d)1 : 1
Explanation
Half lives t 1/2 (A)=20 min; t 1/2 (B)=40 min; Intially, N0 (A)=N0 (B) Total time, T=80 min For radio active substance A For radio active substance B From equations (i) and (ii), Answer:(c)
Q.27
) In which of the the following system will be radius of the first orbit (n=1) be minimum? [ AFMC 2007]
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a) Deuterium atom
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b) hydrogen atom
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c) Doubly ionized lithium
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d) Singly ionised helium
Explanation
Radius of the orbit is inversly proportional to the nuclear charge (Ze) which is maximum in lithium. ∴: In doubly ionised lithium the radius of the first orbit be minimum.Answer: (c)
Q.28
) The fussion of 235 U can be triggered by the absorption of a slow netron by a nucleus. Similarily, a slow proton can also be used.This statment is [ AFMC 2007]
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a)correct
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b) wrong
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c)information is insufficient
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d)none of the above.
Explanation
A slow proton cannot tigger a fission in 235U atom. This statment is wrong.Answer: (b)
Q.29
) Activity of radio active sample decreases to (1/3)rd of its original value in 3 days. Then in 9 days its actvity will become [ AFMC 2008]
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a) (1/27) of the original value
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b) (1/9) of the original value
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c)(1/18) of the original value
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d)(1/3) of the original value
Explanation
Intial activity ( i.e., at t=0 )=A 0 Activity after a time t, is A Answer: (a)
Q.30
) A free neutron decays spontaneously into [ AFMC 2008]
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a) a proton, an electron and anti neutrino
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b) a proton, an electron and a neutrino
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c)a proton and electron
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d)a proton, and electron, a neutrino and an anti-neutrino
Explanation
Answer:(a)
0 h : 0 m : 1 s
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