Nuclei  MCQs

MCQs of Nuclei

Showing 41 to 50 out of 138 Questions
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41.
A sample contains a number of stable nuclei equal to Ns and the number of unstable nuclei equal to Nu. After a time T the activity of the sample decreases to one-third of the initial activity, while the total number of nuclei (excluding decayed nuclei) becomes half. The ratio NsNu initially is _____ .
(a) 13
(b) 14
(c) 3
(d) 2
Answer:

Option (a)

42.
When an electron-positron pair annihilates, the energy released is about ______ .
(a) 0.82 × 10-13 J
(b) 1.64 × 10-13 J
(c) 3.21 × 10-13 J
(d) 4.82 × 10-13 J
Answer:

Option (b)

43.
If the rate of emission of energy from a star is 2.7 × 1036 J/s, the rate of loss of mass in the star will be _____ .
(a) 3 × 1018 kg/s
(b) 3 × 1019 kg/s
(c) 3 × 1020 kg/s
(d) 3 × 1021 kg/s
Answer:

Option (b)

44.
Heavy water is a _____ .
(a) water at 4°C
(b) water in which soap does not lather
(c) compound of deuterium and oxygen
(d) compound of heavy oxygen and heavy hydrogen
Answer:

Option (c)

45.
In atom bomb, the reaction which occurs is _____ .
(a) fusion
(b) thermonuclear
(c) controlled fission
(d) uncontrolled fission
Answer:

Option (d)

46.
Nuclear fusion is possible _____ .
(a) only between light nuclei
(b) only between heavy nuclei
(c) between both light and heavy nuclei
(d) only between nuclei which are stable against β-decay
Answer:

Option (a)

47.
In the process of atomic explosion the maximum energy is present in which form _____ .
(a) γ-rays
(b) kinetic energy of products
(c) infrared region
(d) visible light
Answer:

Option (b)

48.
The weight based ratio of U238 and Pb206 in a sample of rock is 4 : 3. If the half-life of U238 is 4.5 × 109 yr, then the age of rock is _____ .
(a) 9.0 × 109 yr
(b) 6.3 × 109 yr
(c) 4.5 × 109 yr
(d) 4.05 × 109 yr
Answer:

Option (d)

49.
Find the energy released for the nuclear reactionR88226a → Ra88222 + He24. The kinetic energy of emitted α-particles is 4.78 Mev. Assume parent nucleus to be at rest. 
(a) 8 Mev
(b) 4.78 Mev
(c) 4.87 Mev
(d) Information is insufficient
Answer:

Option (c)

50.
The critical mass of U235 can be reduced by _____ .
(a) putting a neutron reflector around it
(b) heating it
(c) mixing impurity in it
(d) putting neutron absorber around it
Answer:

Option (a)

Showing 41 to 50 out of 138 Questions
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