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NCERT Questions for Class 12 Physics Chapter 13 – Nuclei
NCERT Class 12 Physics Chapter 13 – Nuclei important questions is an important resource for students preparing for their board exams. The students who are studying for their examinations can benefit greatly from using these questions as a resource. Obtaining a full comprehension of the issues that are discussed in the chapter can be accomplished by students through the practice of these important questions. The questions address fundamental aspects such as the mass-energy relationship, nuclear force, nuclear fusion, and nuclear fission, as well as the composition and size of the nucleus.
Table of Contents
Important Questions with Solutions of Class 12 Physics Chapter 13 – Nuclei
Short Answer Questions
1) Prove that the density of nuclear matter remains approximately constant, exhibiting minimal dependence on A using the below relation where R0 is a constant and A is the mass number of a nucleus.
Ans – We know,
If m is the average mass of the nucleus then mass of the nucleus = mA
As a result, A is independent of the density of nuclear matter. It is almost constant.
2) Calculate the equivalent energy in electron volts for 16 mg of mass.
Ans – It is known that,
E = mc2
3 Mark Questions
1) A radioactive nuclide decays into a stable nuclide with a half-life of 3 minutes. What fraction of its 1g will remain radioactive after 9 minutes?
Ans – Let the no. of atoms/gram = N0
t = 9 minutes
T1/2 = 3 minutes
Thus, the fraction that remain undecayed = 1 – 0.875 = 0.125
2) Determine the height of the possible barrier for a direct collision between two deuterons. (Hint: When two deuterons just touch, the Coulomb repulsion between them determines the height of the potential barrier. Assume they can be regarded as rigid spheres with a radius of 2.0 fm.)
Ans – When two deuterons collide head-on, the distance between their centres is expressed as:
d = Radius of the first deuteron + Radius of the second deuteron.
Radius of a deuteron nucleus = 2fm = 2 × 10−15 m
⇒ d = 2 × 10−15 + 2 × 10−15
= 4 × 10−15 m
Charge on a deuteron nucleus = Charge on an electron = e = 1.6 × 10−19 C
Potential energy of the two-deuteron system:
ε0 is the Permittivity of free space
3) Determine the half-life time of a radioactive material if its activity returns to its initial value after 30 years.
Ans – We know,
5 Marks Questions
1) Define the half-life and decay constant of a radioactive element. Specify their SI unit. Provide the equation for half-life.
Ans – The duration in which half of the atoms of a radioactive substance decay is referred to as the half-life of that substance. SI unit – second(s)
The radioactive decay constant (λ) is the inverse of the duration required for the quantity of atoms in a radioactive substance to diminish to 36.8% of its initial amount. SI unit – s-1 or min-1
We know that,
2) The wavelength of the initial member of the Balmer series is 6563 Å. Determine the wavelength of the first member of the Lyman series.
Ans – We know,
For first member of Balmer series ni = 3
For first member of Lyman series
From (1) and (2) we get,
Thus 1215.4 Å is the wavelength of the first member of the Lyman series.