NCERT Solutions for class 12 Physics | Chapter 13 - Nuclei

(1) Which of the following statement is not true regarding Einsteins mass energy relation?
[A] Mass disappears to reappear as energy.
[B] Energy disappears to reappear as mass.
[C] Mass and energy are two different forms of the same entity.
[D] Mass and energy can never be related to each other.
Answer: Mass and energy can never be related to each other.
(2) Mass energy equation was propounded by
[A] Newton
[B] Madam Curie
[C] C. V. Raman
[D] Einstein
Answer: Einstein

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(3) The curve of binding energy per nucleon as a function of atomic mass number has a sharp peak for helium nucleus. This implies that helium
[A] can easily be broken up
[B] is very stable
[C] can be used as fissionable material
[D] is radioactive
Answer: is very stable
(4) In γ ray emission from a nucleus
[A] only the proton number changes
[B] both the neutron number and the proton number change
[C] there is no change in the proton number and the neutron number
[D] only the neutron number changes
Answer: there is no change in the proton number and the neutron number
(5) Neutron decay in free space is given as follows

Then the parenthesis [ ] represents a

[A] neutrino
[B] photon
[C] antineutrino
[D] graviton
Answer: antineutrino
(6) The half-life period and the mean life period of a radioactive element are denoted respectively by Th and Tm. Then
[A] Th = Tm
[B] Th > Tm
[C] Th < Tm
[D] Th ≥ Tm
Answer: Th < Tm
(7) The process of radioactive radiations remains unaffected due to
[A] physical changes
[B] chemical changes
[C] electric or magnetic fields
[D] all of the above
Answer: all of the above
(8) Which of the following of a radioactive material is a measure of its instability?
[A] Full life
[B] Mean life
[C] Half life
[D] None of these
Answer: Half life
(9) hree specimens A, B, C of same radioactive element has activities 1 microcurie, 1 rutherford and 1 becquerel respectively. Which specimen has maximum mass?
[A] A
[B] B
[C] C
[D] all have equal masses
Answer: B
(10) Radioactive substance emits
[A] α-rays
[B] β-rays
[C] γ-rays
[D] All of the above
Answer: All of the above
(11) Boron rods in a nuclear reactor are used to
[A] absorb excess neutrons
[B] absorb alpha particle
[C] slow down the reaction
[D] speed up the reaction
Answer: Boron rods absorb excess neutrons.
(12) Fusion reactions take place at high temperature because
[A] atoms are ionised at high temperature
[B] molecules break up at high temperature
[C] nuclei break up at high temperature
[D] kinetic enrgy is high enough to overcome repulsion between nuclei
Answer: kinetic enrgy is high enough to overcome repulsion between nuclei
(13) Control rods used in nuclear reactors are made of
[A] stainless steel
[B] graphite
[C] cadmium
[D] plutonium
Answer: cadmium
(14) Half life of radioactive element depends upon
[A] amount of element present
[B] temperature
[C] pressure
[D] nature of element
Answer: nature of element
(15) The ‘rad’ is the correct unit used to report the measurement of
[A] the ability of a beam of gamma ray photons to produceions in a target
[B] the energy delivered by radiation to a target
[C] the biological effect of radiation
[D] the rate of decay of a radioactive source
Answer: the biological effect of radiation
(16) If a radioactive element is placed in an evacuated chamber, then the rate of radioactive decay will
[A] decrease
[B] remains unchanged
[C] increase
[D] none of these
Answer: remains unchanged
(17) The same radioactive nucleus may emit
[A] all the three α, β and γ one after another
[B] all the three α, β and γ radiations simultaneously
[C] only α and βsimultaneously
[D] only one α, β and γ at a time
Answer: only one α, β and γ at a time
(18) Radioactivity is
[A] irreversible process
[B] self disintegration process
[C] spontaneous
[D] all of the above
Answer: all of the above
(19) Nuclear forces exists between
[A] neutron – neutron
[B] proton – proton
[C] neutron – proton
[D] all of these
Answer: all of these
(20) The mass of an atomic nucleus is less than the sum of the masses of its constituents. This mass defect is converted into
[A] heat energy
[B] light energy
[C] electrical energy
[D] energy which binds nucleons together
Answer: energy which binds nucleons together

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