JEE Physics Nuclei MCQs Set A

Question. The nuclear radius as compared to the atomic radius is of the order
(a) 10^–5
(b) 10^–7
(c) 10^–9
(d) 10^–3

Answer: A

Question. Two nuclei which are not identical but have the same number of nucleons represent
(a) Isobars
(b) IsotonesIsotopes
(c) Isotopes
(d) Isotones

Answer: A

Question. Which of the following pairs of particles cannot exert nuclear force on each other?
(a) All of these
(b) Electron and neutron
(c) Neutron and electron
(d) Proton and electron

Answer: A

Question. When two nuclei of mass X and Y respectively fuse to form a nucleus of mass m alongwith the liberation of some energy, then
(a) X + Y > m
(b) X – Y = m
(c) X + Y = m
(d) X + Y < m

Answer: B

Question. The nuclear force between two nucleons is explained by
(a) Meson exchange theory
(b) Gravitation exchange theory
(c) Quark exchange theory
(d) Photon exchange theory

Answer: A

Question. Nuclear energy is released in fusion reaction, since binding energy per nucleon is
(a) Larger for fusion products than for fusing nuclei
(b) Smaller of fusion products than for fusing nuclei
(c) Same for fusion products as for fusing nuclei
(d) Sometimes larger and sometimes smaller

Answer: A

Question. In nuclear reactions we have the conservation of
(a) Charge, total energy and momentum
(b) Energy only
(c) Mass only
(d) Momentum only

Answer: A

Question. In the radioactive decay of an element it is found that the count rate reduces from 1024 to 128 in 3 minutes. Its half life will be
(a) 1 minute
(b) 2 minute
(c) 3 minute
(d) 5 minute

Answer: A

Question. If a radioactive material remains 25% after 16 days, then its half life will be
(a) 8 days
(b) 64 days
(c) 28 days
(d) 32 days

Answer: A

Question. The count rate of a radioactive source at t = 0 was 1600 count/s and at t = 8 s, it was 100 count/s. The count rate (in counts) at t = 6 s was
(a) 200
(b) 300
(c) 400
(d) 150

Answer: A

Question. A radioactive sample at any instant has its disintegration rate 5000 disintegrations per minute. After 5 minute, the rate is 1250 disintegrations per minute. The decay constant (per minute) is
(a) 0.4 ln 2
(b) 0.2 ln 2
(c) 0.1 ln 2
(d) 0.8 ln 2

Answer: A

Question. A freshly-prepared radioactive source of half-life 2 h emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is
(a) 12 h
(b) 6 h
(c) 24 h
(d) 128 h

Answer: A

Question. The sample of a radioactive substance has 10⁶ nuclei. Its half life is 20 s. The number of nuclei that will be left after 10 s is nearly
(a) 7 × 10⁵
(b) 11 × 10⁵
(c) 2 × 10⁵
(d) 1 × 10⁵

Answer: A

Question. Half life of radioactive element depends upon
(a) The nature of the element
(b) Temperature
(c) Pressure
(d) Amount of element present

Answer: A

Question. Neutrino is a particle which
(a) Has no charge but has spin
(b) Has no charge and no spin
(c) Is charged like an electron and has spin
(d) Has no charge but has mass nearly equal to that of a proton

Answer: A

Question. Heavy water instead of ordinary water is used as a moderator in nuclear reactor because ordinary water
(a) Absorbs neutrons
(b) Accelerates neutron
(c) Cannot slow down neutron
(d) Is expensive

Answer: A

Question. Out of the following, which one is not emitted by a natural radioactive substance?
(a) Neutrons
(b) Helium nuclei with charge equal to that of two protons
(c) Electromagnetic radiations
(d) Electrons

Answer: A

Question. If 1 g hydrogen is converted into 0.993 gm of helium in a thermonuclear reaction, the energy released in the reaction is
(a) 63 × 10¹⁰ J
(b) 63 × 10¹⁴ J
(c) 63 × 10²⁰ J
(d) 63 × 10⁷ J

Answer: A

Question. Thermal neutrons are those whose energy is about
(a) 0.03 eV
(b) 1 MeV
(c) 0.03 MeV
(d) 1 J

Answer: A

Question. Control rods used in nuclear reactors are made of
(a) Cadmium
(b) Plutonium
(c) Graphite
(d) Stainless steel

Answer: A

Question. After 3 hours, only 0.25 mg of a pure radioactive material is left. If initial mass was 2 mg then the half life of the substance is
(a) 1 hr
(b) 0.5 hr
(c) 2 hr
(d) 1.5 hr

Answer: A

Question. Choose the correct statement
(a) The nuclear force becomes weak if the nucleus contains a large number of nucleons
(b) Nuclei with atomic number less than 82 shows a tendency to disintegrate
(c) The nuclear force becomes strong if the nucleus contains too many neutrons compared to protons
(d) The nuclear force becomes strong if the nucleus contains too many protons compared to neutrons

Answer: A

Question. Ten percent of a radioactive sample has decayed in 1 day. After 2 days, the decayed percentage of nuclei will be
(a) 19%
(b) 20%
(c) 100%
(d) 81%

Answer: A

Question. Sample of radioactive element has a mass of 10 gm at an instant t = 0. The approximate mass of this element in the sample after two mean lives is
(a) 1.35 gm
(b) 6.30 gm
(c) 3.70 gm
(d) 2.50 gm

Answer: A

Question. After five half lives percentage of original radioactive atoms left is
(a) 3.125%
(b) 0.2%
(c) 0.3%
(d) 1%

Answer: A

Question. The average binding energy per nucleon in the nucleus of atom is approximately
(a) 8 MeV
(b) 9 MeV
(c) 8 KeV
(d) 8 J

Answer: A

Question. Radioactive nuclei P and Q disintegrate into R with half lives 1 month and 2 months respectively. At time t = 0, number of nuclei of each P and Q is x. Time at which rate of disintegration of P and Q are equal, number of nuclei of R is
(a) 1.25 x
(b) 1.5 x
(c) 1.75 x
(d) x

Answer: A