Video Lecture
Theory For Making Notes
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Practice Questions (Basic Level)
1.
The energy of neutron in thermal equilibrium at room temperature is approximately
(a) 5 eV
(b) 1 eV
(c) 0.1 eV
(d) 0.025 eV.
Ans (d)
2.
1 milligram radium has 2.68 × 1018 nuclei. Its half-life is 1620 year. After 3240 year, how many nuclei would have disintegrated?
(a) 1.82 × 1018
(b) 1.34 × 1018
(c) 0.67 × 1018
(d) 2.01 × 1018.
Ans (d)
3.
Fast neutrons can easily be slowed down by
(a) the use of lead shielding
(b) passing them through heavy water
(c) elastic collision with heavy nuclei
(d) applying strong magnetic field.
Ans (b)
4.
What percentage of a radioactive substance is left after 5 half-live
(a) 31%
(b) 3.12%
(c) 0.3%
(d) 1%
Ans (b)
5.
Radon has 3.8 day as its half-life. How much radon will be left out of 15 mg mass after 38 day?
(a) 1.515 mg
(b) 0.015 mg
(c) 1.049 mg
(d) 9.327 mg
Ans (b)
Practice Questions (JEE Main Level)
1.
An element A decays into element C in two steps as
\text{A}\to \text{B}+{{\,}_{\text{2}}}\text{H}{{\text{e}}^{\text{4}}}and \text{B}\to \text{C}+{{2}_{{-\text{1}}}}e{}^\circ then,
(a) A and C are isotopes
(b) A and C are isobars
(c) A and B are isotopes
(d) A and B are isobars.
Ans (a)
2.
A stationary radioactive nucleus of mass 210 unit disintegrates into an alpha particle of mass 4 unit and residual nucleus of mass 206 unit. If the kinetic energy of the alpha particle is E, the kinetic energy of the residual nucleus is
(a) \left( {\frac{2}{{105}}} \right)\,E
(b) \left( {\frac{2}{{103}}} \right)\,E
(c) \left( {\frac{{103}}{{105}}} \right)\,E
(d) \left( {\frac{{103}}{2}} \right)\,E.
Ans (b)
3.
At any instant, the ratio of amount of radioactive substances is 2 : 1. If their half-lives be respectively 12 and 16 hours, then after two days, what will be the ratio of substances?
(a) 1 : 1
(b) 2 : 1
(c) 1 : 2
(d) 1 : 4
Ans (d)
4.
After a certain lapse of time, fraction of radioactive polonium undecayed is found to be 12.5% of the initial quantity. What is the duration of this time lapsed if the half life of polonium is 138 days?
(a) 124 day
(b) 414 day
(c) 345 day
(d) 534 day
Ans (b)
5.
For every 106 atoms of radium in a sample today, find the number of atoms that will be left after 3200 year. Assume half-life of radium to be 1600 year.
(a) 0.5 × 105 atoms
(b) 3.7 × 105 atoms
(c) 2.5 × 105 atoms
(d) 1.3 × 105 atoms
Ans (c)
6.
The radioactive isotope _{{27}}^{{60}}Co is used in the treatment of tumors. It undergoes
Β decay with a half-life of 5.25 y. What is the initial decay rate of a 0.01 g sample?
(a) 0.2 x 1011Bq
(b) 3.7 x 1011Bq
(c) 4.2 x 1011Bq
(d) 5.7 x 1011Bq
Ans (c)
7.
The decay rate of a freshly prepared sample is 15 \displaystyle \mu Ci. It drops to 9 \displaystyle \mu Ci after 2.5 h.
(a)
Find the half-life of the nuclide.
(a) 3.9 h
(b) 5.7 h
(c) 2.8 h
(d) 3.4 h
Ans (d)
(b)
How many radioactive atoms were initially present?
(a) 2.7 x 109
(b) 9.8 x 109
(c) 0.3 x 109
(d) 1.5 x 109
Ans (b)
Practice Questions (JEE Advance Level)
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