CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma

CBSE CLASS XII

Nuclei

Q.1) A nucleus of mass number A has a mass defect . Give the formula, for the binding energy per nucleon of this nucleus? ( 1 mark )

(Q.2) What is the value of atomic mass unit (a.m.u) ( 1 mark )

(a) 1.66x10^-27 kg
(b) 2.66x10^-27 kg
(c) 6.023x10^-27 kg
(d) 2.44x10^-27 kg

(Q.3) Write the relation between half-life and decay constant of a radioactive sample? ( 1 mark )

(Q.4) Which part of the atom emits radioactive radiations? ( 1 mark )

(Q.5) Define binding energy of a nucleus. ( 1 mark )

(Q.6) What are the number of protons and the number of neutrons in a nucleus of ? ( 1 mark )

(Q.7) You are given two nuclides and. Are they the isotopes of same element? Why? ( 1 mark )

(Q.8) Two nuclei have mass numbers in the ratio 1:2. What is the ratio of their nuclear densities? (H) ( 1 mark )

(Q.9) Name the reaction responsible for energy production in the sun. ( 1 mark )

(Q.10) Write the relation between half-life and decay constant of a radioactive sample? ( 1 mark )

(Q.11) What is mass defect? ( 1 mark )

(Q.12) Choose the suitable condition in order to carry out the nuclear reaction
₁H¹ + ₁H¹+₁H² = ₂H4+₁e⁰+ energy (H) ( 1 mark )

(a) very high temperature and moderate pressure will be necessary
(b) moderate temperature and relatively high pressure will be necessary
(c) very high temperature and relatively high pressure would be necessary
(d) very high temperature and low pressure would be necessary

(Q.13) T is the half life period and T_a is the average life of a radioactive substance. Which of the following statement is correct? (H) ( 1 mark )

(a) T > T_a
(b) T is about 69% of T_a
(c) T is inversely proportional to T_a
(d) T and Ta both are directly proportional to radioactive decay constant.

(Q.14) If a proton is completely converted into energy, the amount of energy produced will be (1 mark )

(a) 6.61 X 10³⁴ eV
(b) 6.02 X 10²³ eV
(c) 9 X 10²⁰ eV
(d) 931 X 10⁶ eV

(Q.15) A certain radioactive substance has a half-life of 10 years. If N₀ be the number of nuclei initially then the number of nuclei after 20 years is (H) ( 1 mark )

(a) 1 / N₀
(b) 1 / 4 N₀
(c) N₀
(d) 3 / 4 N₀

(Q.16) Which of the following sequence for the emission of radioactive radiations are followed for a given reaction? (H) _ZX^A   →  _Z+1Y^A   →   _Z-1K^A-4

(a) α , β , α
(b) β , α , γ
(c) γ, α , β,
(d) γ, β , α

(Q.17) A radioactive isotope _ZX^A decays in series by emitting particles and particles. The resultant isotope will be ( 1 mark )

(Q.18) What would be the possible no. of elements if in nature elements with principal quantum number n > 4 were not allowed? ( 1 mark )

(a) 60
(b) 4
(c) 32
(d) 64

(Q.19) Choose the best option for binding energy/nucleon if nuclear energy is released in fission. Binding energy is (1 mark)

(a) smaller for fission fragments than for parent nucleus
(b) same for fission fragments and parent nucleus
(c) larger for fission fragments than for parent nucleus
(d) sometimes larger and sometimes smaller

(Q.20) What will be the amount of energy released if a microgram of a matter is converted into energy? ( 1 mark )

(a) 9 X 10¹⁴ joule
(b) 9 X 10⁴ joule
(c) 9 X 10⁷ joule
(d) 9 X 10¹⁰ joule

(Q.21) By how much fraction energy will be decreased in a given atomic explosion, if the speed of light were become 1/3 of the present value? ( 1 mark )

(a) 8/9
(b) 1/9
(c) 1/3
(d) 2/3

(Q.22) Let the velocities of light in vacuum and glass are represented by v and v_g. When electrons move through glass with a velocity v_e, there emitted a visible radiation in glass if ( 1 mark )

(a) v_e > v_g
(b) v_e < v_g
(c) v_e < v
(d) v_e < v_g/ v

(Q.23) After one -decay and two consecutive -decays, the daughter nucleus is an isotope of the ( 1 mark )

(a) same element
(b) element with atomic numbers less by two
(c) element with atomic numbers more by two
(d) element with same atomic no. but different mass no.

(Q.24) Which of the following is more effective for producing nuclear reactions with nuclei compared to protons? ( 1 mark )

(a) neutrons
(b) alpha particles
(c) electrons
(d) beta particles

(Q.25) Which of the following can't be used as a moderator for a nuclear reactor? ( 1 mark )

(a) Paraffin
(b) Heavy water
(c) Silicon
(d) Graphite

(Q.26) If the effective decay constant of the nucleus is and if it will decay simultaneously by two different processes having decay constants , then (H) ( 1 mark )

(Q.27) Choose the correct option regarding a ^β-decay (H) ( 1 mark ) n  → p + e^- + v^-

(b) In beta-plus decay, a proton transforms into a neutron inside the nucleus according to p  → n + e⁺ + v^-

(c) In beta-minus decay, a neutron transforms into a proton within the nucleus according to n  → p + e⁺ + v

(d) In beta-plus decay, a neutron transforms into a proton inside the nucleus according to n  → p + e^- + v^-

(Q.28) Which one of the following is S.I unit of radioactivity? ( 1 mark )

(a) Becquerel
(b) Decay per second
(c) Curie
(d) Rutherford

(Q.29) Energy released in the fission of a single nucleus is 200 MeV. The fission rate of a filled reactor at a power level of 6 W is ( 1 mark )

(a) 1.8 X 10¹⁰ /s
(b) 1.87 X 10¹⁶ / s
(c) 1.87 X 10¹¹ / s
(d) 1.87 X 10¹⁷ / s

(Q.30) The half life period of a sample is 100 second. If we take 40 gm of the radioactive sample, then after 400 second how much substance will be left undecayed? ( 1 mark )

(a) 1.25 gm
(b) 5 gm
(c) 10 gm
(d) 2.5 gm

(Q.31) The activity of a radioactive sample decreases to one-third of the original value in 9 years. What will be the activity after further 9 years ? ( 1 mark )

(a) A₀ / 3
(b) A₀ / 6
(c) A₀ / 9
(d) A₀ / 18

(Q.32) Intensity of gamma rays falls to one-eight of its value after passing through 27 mm of lead. What should be the thickness of the lead sheet to reduce the intensity to half? ( 1 mark )

(a) 24 mm
(b) 18 mm
(c) 12 mm
(d) 9mm

(Q.33) If a particle is being added to the nucleus of an atom but not changing its chemical properties. Then, these particles are ( 1 mark )

(a) alpha particles
(b) neutrons
(c) protons
(d) electrons

(Q.34) What would be the atomic mass of the most suitable element for nuclear fission? ( 1 mark )

(a) 11
(b) 21
(c) 92
(d) 52

(Q.35) If the mass defect during the formation of lithium from hydrogen is 0.5%, what will be the energy obtained in forming lithium from 1 kg of hydrogen? (H) ( 1 mark )

(a) 1.25
(b) 1.35
(c) 1.25 × 10⁸
(d) 1.35 × 10⁸

(Q.36) The volume of the nucleus having a mass number A is directly proportional to (1 mark)

(a) A^1/3
(b) A³
(c) A
(d) A²

(Q.37) Tritium has a half life of 12.5 years against beta decay. What friction of a sample of pure tritium will remain undecayed after 25 years? ( 1 mark )

(a) 1/4th
(b) 1/2th
(c) 1/8th
(d) 1/16th

(Q.38) The mass defect in a nuclear fusion reaction is 0.5 %. What amount of energy will be liberated in one kg fusion reaction? ( 1 mark )

(a) 2.7x10¹⁴ joule
(b) 2.1x1016 joule
(c) 4.7x10¹⁴ joule
(d) 4.5x10¹⁴ joule

(Q.39) In ₈₈Ra²²⁶ nucleus, there are ( 1 mark )

(a) 138 protons and 88 neutrons
(b) 138 neutrons and 88 protons
(c) 226 protons and 88 electrons
(d) 226 neutrons and 138 electrons

(Q.40) A radio active substance decays to 1/16^th of its initial activity in 40 days. The half life of the radioactive substance expressed in days is ( 1 mark )

(a) 20
(b) 5
(c) 10
(d) 2.5

(Q.41) State two properties of nuclear forces? ( 2 Marks )

(Q.42) What is the energy equivalent of 10 mg mass? (H) ( 2 Marks )

(Q.43) Plutonium decays with a half cycle of 24000 years. If the plutonium is stored for 72000 years, what fraction of it remains ? (H) ( 2 Marks )

(Q.44) Name the reaction which takes place when a slow neutron beam strikes nuclei. Write the nuclear reaction involved. (2 Marks )

(Q.45) Calculate the energy released in the following nuclear reaction:
Given: Mass of

( 3 marks )

(Q.46) Define decay constant of a radioactive sample. Which of the following radiations α-rays,β- rays, and γ - rays,

(i) Are similar to X-rays? s
(ii) Are easily absorbed by matter?
(iii) Travel with greatest speed?
(iv) Are similar in nature to cathode rays? ( 3 Marks )

(Q.47) Calculate the binding energy of an α- particle from the following data:

Mass of free proton=1.007825 a.m.u.
Mass of free neutron=1.008665 a.m.u.
Mass of helium nucleus=4.002800 a.m.u.
Take 1 a.m.u=931.5 MeV. ( 3 Marks )

Q.48) What are the different kinds of radioactive decay that exist in nature? (H) ( 3 Marks )

(Q.49) Draw a labeled diagram of a nuclear reactor and write the function of each part. (5Marks )

(Q.50) Distinguish between nuclear fission and fusion.

Submitted By Mr. Ajay Sharma
Email Id : [email protected]