Physics

Nuclear and Atomic Physics

571 Questions

Nuclear and atomic physics explores the components and properties of the nucleus, including isotopes, radioactive decay, and fundamental forces. These concepts are essential for various competitive exams requiring a strong foundation in physics. The provided questions cover structural properties, mass, energy equivalence, and particle interactions.

Nucleus propertiesIsotopes and mass numberAlpha particle scatteringNuclear forcesMass energy equivalenceBeta particle emission

Nuclear and Atomic Physics Questions

Multiple choice chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

Radius of a nucleus is proportional to:

  1. $A$
  2. ${A}^{{1}/{3}}$
  3. ${A}^{2}$
  4. ${A}^{{2}/{3}}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Radius of a nucleus is proportional to $\displaystyle {A}^{{1}/{3}}$
$\displaystyle r=(1.4 \times 10^{-15}) \times {A}^{{1}/{3}}$
Where r is the radius of the nucleus with mass number A.
Here, the unit of radius is meters.  

Multiple choice chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

The ratio of the volume of the atom and the volume of the nucleus is:

  1. ${10}^{10}$
  2. ${10}^{12}$
  3. ${10}^{15}$
  4. ${10}^{20}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The ratio of the volume of the atom and the volume of the nucleus is $\displaystyle 10^{15}$

The radius of an atomic nucleus is of the order of $\displaystyle {10}^{-13} cm$ or $\displaystyle {10}^{-15} m$ or one Fermi unit.

On the other hand, the radius of an atom is of the order of $\displaystyle {10}^{-8} cm$ or $\displaystyle {10}^{-10} m$ or one angstrom unit.

Note:
The radius of nucleus is much smaller than atomic radius.

The ratio of atomic radius to radius of nucleus is $\displaystyle \dfrac {{10}^{-10} m}{{10}^{-15} m}=10^5$

Volume is proportional to cube of radius.

The ratio of atomic radius to radius of nucleus is $\displaystyle  (10^5)^3 = 10^{15}$

Multiple choice chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

Which is characteristic of unstable nucleus?

  1. $n/p$ ratio is high

  2. Low binding energy

  3. High packing fraction

  4. None of these
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

It is the balance of protons and neutrons in a nucleus which determines whether a nucleus will be stable or unstable. Other factors that influence the stability of nucleus are binding energy and high packing fraction. 

So, the characteristics of unstable nucleus are
  1. $\dfrac{n}{p}$ ratio is high
  2. Low binding energy
  3. High packing fraction

Multiple choice chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

The density of nucleus is of the order of:

  1. ${ 10 }^{ 5 }kg{ m }^{ -3 }$
  2. ${ 10 }^{ 10 }kg{ m }^{ -3 }$
  3. ${ 10 }^{ 17 }kg{ m }^{ -3 }$
  4. ${ 10 }^{ 25 }kg{ m }^{ -3 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The density of nucleus is about $2.3\times { 10 }^{ 17 }{ ㎏ }/㎥$. The density is same for all nuclei. Thus density of nucleus is of the order ${ 10 }^{ 17 }{ ㎏ }/㎥$

Multiple choice chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

The radius of nucleus is:

  1. proportional to its mass number

  2. inversely proportional to its mass number

  3. proportional to the cube root of its mass number

  4. not related to its mass number
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The radius of a nucleus (r) is proportional to the cube root of its mass number (A).
The approximate law is $r = r _0 \times A^{ 1/3 }$
where $r _0 = 1.2 \times 10^{ -15 }\ m$
option C is correct
Multiple choice physics behaviour of perfect gas and kinetic theory of gases mean free path law of equipartition of energy and mean free path behavior of perfect gas and kinetic theory

Estimate the mean free path of a cosmic ray proton in the atmosphere at sea level. Given $\sigma = 10 ^{-26} cm^2$

  1. $10^4 cm$
  2. $10^{-4} cm$
  3. $10^6 cm$
  4. $10^{-6} cm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The mean free path is given by, $\lambda=\dfrac{1}{\pi \sigma n}$

Here the proton is scattered by the molecules of the atmosphere. 
The density of the molecules of the atmosphere is $n=\dfrac{N}{V}=\dfrac{P}{kT}=\dfrac{10^6}{(1.38\times 10^{-16})(300)}=2.4\times 10^{19}$  (all units are taken in CGS unit)
So, $\lambda=\dfrac{1}{\pi(10^{-26})(2.4\times 10^{19})}=1.3\times 10^6\sim 10^6 $  $cm$

Multiple choice physics life cycle of stars evolution and end stages of stars the stars stars

How many helium nuclei fuse together when making carbon?

  1. 2

  2. 3

  3. 4

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

At sufficiently high temperatures and densities, a 3-body reaction called the triple alpha process can occur: Two helium nuclei ("alpha particles") fuse to form unstable beryllium.

If another helium nucleus can fuse with the beryllium nucleus before it decays, stable carbon is formed along with a gamma ray.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The charge to mass ratio of $\alpha - particle$ is approximately ____  of the charge to mass ratio of a proton is:

  1. half

  2. twice

  3. 4 times

  4. 6 times
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Alpha particle is a helium nucleus containing two protons and two neutrons so its charge is $twice$ the proton’s charge while the mass is about 4 times greater.
Let the charge of the proton be $+e$, then the charge of the alpha particle will be $+2e$. Similarly mass of the proton be m, then the mass of the alpha particle will be $4m$.
Specific charge = charge/mass of the substance.
For proton, specific charge =$\dfrac { e }{ m } $
For alpha particle, specific charge = $\dfrac { 2e }{ 4m } $
Therefore the ratio is = $\dfrac { e }{ m } $ x $\dfrac { 4m }{ 2e }  = 2:1$
Hence, the charge to mass ratio of an alpha particle is approximate twice the charge to mass ratio of a proton.  
So, the correct option is $B$
Multiple choice physics nuclei nuclear force the nuclear force nuclear force and binding energy

The binding energy per nucleon for $\mathrm { U } ^ { 238 }$ about 7.5Mev where as it is about 8.5 Mev for a nucleus having a mass half of Uranium. If $\mathrm { U } ^ { 238 }$ splits into two exact halves the energy released would be

  1. 6.4 Mev

  2. 119 Mev

  3. 238 Mev

  4. 476 Mev
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Energy released = (Total binding energy of products) - (Total binding energy of reactants). Reactants: 238 nucleons * 7.5 MeV = 1785 MeV. Products: 2 * (119 nucleons * 8.5 MeV) = 2023 MeV. Energy released = 2023 - 1785 = 238 MeV.

Multiple choice physics nuclei nuclear force the nuclear force nuclear force and binding energy

Let $F _{pp},F _{pn}$ and $F _{nn}$ denote the magnitudes of the nuclear force by a proton on a proton, by a proton on a neutron and by a neutron on a neutron respectively when the separation is less than one Fermi. Then

  1. $F _{pp}>F _{pn}= F _{nn}$
  2. $F _{pp}=F _{pn}= F _{nn}$
  3. $F _{pp}>F _{pn}> F _{nn}$
  4. $F _{pp}< F _{pn}= F _{nn}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

At separation less than one fermi,  the nuclear force of attraction is strongly active and Nuclear force is charge independent force.

Hence , $F _{pp} = F _{pn} = F _{nn}$