WBBSE Class 10 Physical Science Solutions Chapter 7 Atomic Nucleus

Detailed explanations in West Bengal Board Class 10 Physical Science Book Solutions Chapter 7 Atomic Nucleus offer valuable context and analysis.

WBBSE Class 10 Physical Science Chapter 7 Question Answer – Atomic Nucleus

Very Short Answer Type Questions :

Question 1.
Out of α, β and γ rays which one is called hand rays?
Answer:
γ-rays

Question 2.
Out of α, β and γ-rays which one causes maximum damage to the body tissues ?
Answer:
α-rays.

Question 3.
What is the density of nucleus?
Answer:
10¹⁴ / cm³

Question 4.
What is the binding energy for a mass defect of 1 amu?
Answer:
931.5 Mev.

Question 5.
What is the n / p ratio of lighter nuclides ( Z up to 20 )?
Answer:
1.

Question 6.
What is the n / p ratio of \({ }_1^1 \mathrm{H}\) ?
Answer:
0 .

Question 7.
What is the n / p ratio of \({ }_{83}^{209} \mathrm{Bi}\) ?
Answer:
1.52 .

Question 8.
Which emission increases n/p ratio?
Answer:
positron.

Question 9.
Which emission decreases n/p ratio?
Answer:
β-rays

Question 10.
What is the value of packing fraction for stable nuclides?
Answer:
Zero or negative.

Question 11.
What is the value of packing fraction for unstable nuclides?
Answer:
positive.

Question 12.
What are the magic numbers?
Answer:
Magic numbers are 2, 8, 20, 50, 82 and 126.

Question 13.
Do nuclear forces obey inverse square law?
Answer:
Nuclear forces are not governed by inverse square law.

Question 14.
What is the cause of nuclear isomerism?
Answer:
Nuclear isomerism arises because of the difference in arrangement of nucleons and difference in energy of nucleons.

Question 15.
Is rate of nuclear decay dependent of concentration, pressure and temperature?
Answer:
Rate of nuclear decay is independent of concentration, pressure and temperature.

Question 16.
What is the life span of a radioactive element?
Answer:
The life span of a radioactive element is infinite.

Question 17.
Is the half-life of a radioactive element dependent of its physical and chemical state?
Answer:
The half-life of a radioactive element is independent of its physical and chemical state.

Question 18.
What is the end product of (4n + 1) series?
Answer:
In (4n+1) series, the end product is bismuth.

Question 19. What is the end product of 4 n series?
Answer:
The end product of 4 n series is lead.

Question 20.
Why (4n+1) series is called neptunium series though this series starts from plutonium?
Answer:
The (4n+1) series actually starts from plutonium but is called neptunium series because neptunium is the longest lived isotope of the series.

Question 21.
What is the starting element of (4n + 3) series?
Answer:
The (4n+3) series starts from \({ }_{92}^{235} \mathrm{U}\).

Question 22.
Is there any change is group number during a and b-emissions in case of lanthanides and actinids?
Answer:
There is no change in group number during α and β-emissions in case of lanthanides and actinides.

Question 23.
How many a and b particles are emitted from thorium series?
Answer:
The thorium series emits 6 α and 4β particles.

Question 24.
How many a and b particles are emitted from uranium series?
Answer:
The uranium series emits 8 α and 6β particles.

Question 25.
Name the natural radioaclive series.
Answer:
The 4n, (4n+2),(4n+3) are natural radioactive series.

Question 26.
What is artificial series?
Answer:
(4n+1) is artificial series.

Question 27.
What is the cause of b-emission?
Answer:
β-particle emission is due to breaking down of a neutron into a proton and an electron.

Question 28.
What is the relation of nuclear forces with electrostatic forces?
Answer:
The nuclear forces are about 10²¹ times as strong as the electrostatic forces.

Question 29.
What is the (n/p) ratio of \({ }_1^3 \mathrm{H}\) ?
Answer:
The (n/p) ratio of \({ }_1^3 \mathrm{H}\) is 2.0.

Question 30.
What amount of energy is released during the fission of an atom of \({ }^{235} \mathrm{U}\) ?
Answer:
The fission of an atom \({ }^{235} \mathrm{U}\) releases 211.5MeV of energy.

Question 31.
What are the uses of P-32, Co-60, Na-24, I-131?
Answer:

• P-32 : Leukemia (Blood cancer)
• Co-60 : Treatment of tumar and cancer
• Na-24 : Circulation of blood.
• I-131 : Treatment of gioter (Hyper thyroidism)

Question 32.
Why Nuclear fusion reactions are called thermonuclear reactions?
Answer:
Nuclear fusion reactions require very high temperature (≈10⁶ K) these are therefore, known as thermonuclear reactions.

Question 33.
What are the types of meson particles?
Answer:
The meson particles are of three types

1. Positive meson (π⁺)
2. Negative meson (π^–)
3. Neutral meson (π⁰)

Question 34.
What are the factors on which stability of nucleus depends?
Answer:
The stability of the nucleus is governed mainly by mass defects, binding energy, magnetic numbers and n / p ratio.

Question 35.
How mass defect can be converted into energy?
Answer:
The mass defect can be converted into energy by using Einstein equation ΔE = m c².

Question 36.
What is called binding energy?
Answer:
Binding energy is the energy which binds the nucleons together and binding energy divided by the number of nucleons gives binding energy per nucleon, used to compare the stability of various nuclei.

Question 37.
Who discovered natural radioactivity?
Answer:
Natural radioactivity was discovered by Henry Becquerel.

Question 38.
What is the effect of mass number and atomic number during emission of a-particle?
Answer:
The emission of α-particle decreases the mass number by 4 unit and decreases atomic number by two unit.

Question 39.
State the different unit of rate of decays.
Answer:
nit of rate of decays are :

• 1 Curie (c) = 3.7 × 10¹⁰ dps
• 1 Rutherford (Rd) = 10⁶ dps
• 1 Becquerel (Bq) = 1 dps

Question 40.
What is the use of carbon dating?
Answer:
Carbon dating is used to determine the age of wood, animal fossils etc having carbon.

Question 41.
What are the parts of nuclear reactor?
Answer:
Nuclear reactor consists of –

• A fissionable material → Pu or \({ }^{235} \mathrm{U}\)
• A moderator → Graphite or D₂O to slow down of neutrons.
• Control rods → B, steel or Cd to capture some neutrons.
• Coolent → Heavy water or sodium or an alloy of Na and K (used to carry away the heat)

Question 42.
What happens when Δ-ray is emitted from an atom?
Answer:
When Δ-ray is emitted from an atom, no new element is produced. It results in a change in the energy state of the nucleus.

Question 43.
What is β-ray?
Answer:
β-ray is nothing but a stream of fast moving electrons with a negative charge of 1.6 × 10^-19 coulomb.

Question 44.
Which element is formed when an α-particle takes up two electrons?
Answer:
When an α-particle (He²⁺) takes up two electrons, the element Helium (He) is formed.

Question 45.
Name a radioactive inert element.
Answer:
The inert gas Radon (Rn) with atomic number, Z = 86, is a radioactive inert element.

Question 46.
Name an instrument to record radioactive emissions.
Answer:
Geiger Counter is an instrument used to record the rate of emission from radioactive substance.

Question 47.
Which nuclear reaction takes place inside the sun?
Answer:
The enormous amount of heat energy produced in the sun is due to the thermonuclear fusion reactions taking place in the core of the sun.

Question 48.
What is the role of a neutron in nuclear fission?
Answer:
When a neutron (nuclear projectile) is absorbed by a nucleus, it provides energy that destabilizes the nucleus leading to fission.

Question 49.
Is the mass per nucleon of a nucleus greater than, less than or the same as the mass of a nucleon outside the nucleus?
Answer:
The mass per nucleon is greater outside the nucleus.

Question 50.
Why is neutron a better nuclear projectile than a proton or an electron?
Answer:
Neutron has no charge, so it dges not experience electrostatic forces from surrounding nucleons. It can thus penetrate further before colliding with other particles.

Question 51.
Mention the function of heavy water in a nuclear reaction.
Answer:
Heavy water (D₂O) is used as moderator and coolant in a nuclear reactor. It is the best moderator avalable.

Short Answer Type Questions :

Question 1.
What are nuclear reactions?
Answer:
Nuclear reactions: Nuclear reactions are the reactions in which nucleons of an atom undergo a change.

Question 2.
What do you mean n y ‘isotopes’?
Answer:
Isotopes: The atoms of an element having same atomic number but different mass number are called isotopes.
Example :
\({ }_1^1 \mathrm{H}, \quad{ }_1^2 \mathrm{H}, \quad{ }_1^3 \mathrm{H}\)

Question 3.
What are nuclear isomers?
Answer:
Nuclear isomers: The nuclear species having same atomic number and same mass number but different radioactive properties are called nuclear isomers.
Examples : \({ }^{69} \mathrm{Zn}\)(t^1/2 = 13.8 hour) nd \({ }^{69} \mathrm{Zn}\) (t^1/2 = 57 minute)

Question 4.
What is isoster?
Answer:
Isoster: Molecules or ions with same number of atoms and also the same number of electrons are said to form isosteric group or more simply isosters.
Examples : N₂O and CO₂

Question 5.
What do you mean by nuclear forces?
Answer:
Noclear forces: The forces which held the nucleons together within the small nucleus are called nuclear forces.
These force exist among p-p, p-n and n-n.

Question 6.
What is packing fraction ?
Answer:
Packing fraction: Packing fraction was proposed by Aston and defined as the difference of actual isotopic mass and the mass number.

Question 7.
What are magic numbers ?
Answer:
Magic numbers: Magic numbers are the numbers 2, 8, 20, 50, 82 and 126 . Nuclides having magic number of either proton or neutrons or both are more stable.

Question 8.
What is Radioactivity ?
Answer:
Radioactivity : It is a process in which nucleus of certain elements undergo spontaneous disintegration without excitation by any external means.

Question 9.
What do you mean by ‘Group Displacement Law’?
Answer:
Group Displacement Law : We know that an α-emission decreases the atomic number of the parent by 2 and β-emission increases the atomic number by 1 .
Thus ‘In an α-emission, the parent element will be displaced to a group two places to the left and in β-emission, it will be displaced to a group one place to the right’.

Question 10.
What are disintegration series ?
Answer:
Disintegration series: The whole series of elements starting with the parent radioactive element to the stable end product is called a radioative disintegration series. These series are-
4n(4n + 1),(4n + 2) and (4n+3)

Question 11.
What is half-life period ?
Answer:
Half-life period: Half-life period of a radioactive isotope is the time required for one-half of the isotope ot decay.
t^1/2 = \(\frac{0.693}{\lambda}\) (λ = disintegration constant)

Question 12.
What do you mean by ‘Rutherford’?
Answer:
Rutherford : If a radioactive substance has 10⁶ discitegrations per second, it is said to have an activity of one Rutherford.

Question 13.
What is Radioactive equilibrium ?
Answer:
Radioactive equilibrium: Radioactive change being an irreversible process shows equilibrium when a daughter element disintegrates at the same rate at which it is formed from parent element.

Question 14.
What is ‘Articicial radioactivity’ ?
Answer:
Artificial radioactivity : It is the phenomenon in which artificial transmutation of a stable nucleus leads to the formation of a radioactive nuclide.

Question 15.
What do you mean by ‘Alchemy’?
Answer:
Alchemy: The process of transforming one element into other is known as alchemy and the person involved in such experiments is called alchemist.

Question 16.
What is spallation reaction ?
Answer:
Spallation reaction: High speed projectiles with energies approximately 40 \mathrm{MeV} may chip fragments from a heavy nucleus, leaving a small nucleus. This type of reaction is called spallation
Examples :

Question 17.
What is nuclear fusion?
Answer:
Nuclear fusion : A nuclear reaction in which two lighter nuclei are fused together to form a heavier nuclei is called nuclear fusion.
Examples :

Question 18.
What is Nuclear fission?
Answer:
Nuclear fission : The process of artificial transmutation in which heavy nucleus is broken down into two lighter nucli of nearly comparable masses with release of large amount of energy is termd as nuclear fission.
Examples :

Question 19.
What is meant by ‘projectile capture reactions’?
Answer:
Projectile capture reaction: The bombarding particle is absorbed with or without the emission of γ-radiations.
Examples :

Question 20.
What is Natural transmutation?
Answer:
Natural transmutation: It is a process in which elements such as radium undergoes transmutation on their own.

Broad Answer Type Questions :

Question 1.
What are the symbol, mass and charges of electron,proton and neutron?
Answer:

Question 2.
What do you mean by Isobars and Isotones ?
Answer:
Isobars : The nuclides of different chemical elements having same mass number but different atomic numbers are called isobars.
Examples : \({ }_{18}^{40} \mathrm{Ar},{ }_{19}^{40} \mathrm{~K},{ }_{20}^{40} \mathrm{Ca}\)
Isotnes: The nuclides of different chemical elements having the same number of neutrons but different atomic numbers are called isotones.
Examples : \({ }_1^3 \mathrm{H},{ }_2^4 \mathrm{He}\)

Question 3.
What are the nature, penetrating power and ionising power of a, b, g ravs.
Answer:

Question 4.
What do you mean by ‘Binding energy’?
Answer:
Binding energy-Atomic nucleus is made of protons and neutrons closely is a small volume. Although there exist intensive repulsive forces between the component protons, the nucleus is not slit apart. This is so because the nucleons are bound to one another by very powerful forces. The energy that binds the nucleus together in the nucleus is called the nuclear binding energy.

Question 5.
What are the parent and end product of different disintegration series?
Answer:

Question 6.
What do you mean by ‘Curie’ and ‘Becquerel’?
Answer:
Curie : If a radioative substance disintegrates at the rate of 37 × 10¹⁰ disintegrations per second, its activity is said to be 1 curie.
Becquerel (SI unit) : If a radioactive substance has 1 disintegration per second, it is said to have an activity of one Becquerel.

Question 7.
Give differences between Nuclear Reactions and Chemical Reactions.
Answer:
Difference between Nuclear Reactions and Chemical Reactions.

Nuclear Reactions	Chemical reactions
i. Proceed by distribution of nuclear particles	i. Proceed by the rearrangement of extranuclear electrons.
ii. One element may be converted into another.	ii. No new element can be produced.
iii. Rate of reaction is unaffected by external factors such as concentration temperature, pressure and catalyst.	iii. Rate of reaction is influenced by external factor.

Question 8.
What are the differences between nuclear fission and nuclear fusion.
Answer:
Difference between nuclear rission and nuclear fusion.

Nuclear fission	Nuclear fusion
i. A bigger nucleus splits into smaller nuclei.	i. Larger nuclei fuse together to form the heavier nucleus.
ii. It does not require high temperature	ii. Extremely high temperature is required
iii. A chain reaction sets in.	iiii. It is not a chain reaction.

Numerical Problems :

Example 1:
What is the packing fraction of \({ }_{26}^{56} \mathrm{Fe}\) (isotope mass =55.92066 )?
Answer:
Packing fraction = \(\frac{\text { (isotopic mass – mass number) }}{\text { mass number }}\) × 10⁴
= \(\frac{(55.92066-56)}{560}\) × 10⁴ = -14.167
So, the packing fraction of \({ }_{26}^{56} \mathrm{Fe}\) is -14.167.

Example 2:
How many α and β-particles wil be emitted by \({ }_{84}^{218} \mathrm{Ra}\) in changing to \({ }_{82}^{206} \mathrm{~Pb}\) ?
Answer:
Let x and y be the number of α and β-particles involved in bringing about the change

Comapring the mass number = 218 = 206 + 4x + 0y
4 x = 12
x = 3
or,
x = 3
comparing the atomic numbers
84 = 82 + 2x – y
2x – y = 2
y = 4
The number of α nd β-particles emitted in the given nuclear reaction is 3 and 4.

Example 3.
Calculate the number of neutrons in the remaining atom after emission of an α particle from \({ }^{238}{ }_{92} \mathrm{U}\) atom.
Answer:
On emission of an α-particle atomic mass
of daughter element = 238 – 4 = 234
atomic number of daughter element = 92 – 2 = 90
Number of neutron = Atomic mass – atomic number = 234 – 90 = 144

Example 4:
A radioactive substance decays at such a rate that after 46 days only 0.25 of its original amount is left. Calculate its disintegration constant.
Answer:
Let, the original amount be NO, then
Amount after 46 days, N_t =0.25 × N0
For a nuclear decay

Example 5 :
A certain nuclide has a helf-life of 60 min. If a sample containing 600 atoms is allowed to decay for 90 min, what will be the remaining atoms?
Answer:

Example 6 :
The activity of a sample of radioactive element A¹⁰⁰ is 6.02 curie. Its decay constant is 3.7 × 10⁴ S^-1. Calculate the initial mass of the sample.
Answer:

Example 7:
At radioactive equilibrium, the ratio between the atoms at two radioactive elements A and B was found to be 3.1 × 10⁹: 1 respectively. If t_1/2 of element A is 2 × 10¹⁰ year then what will be the t_1/2 of the element B ?
Answer:
At radioactive equilibrium

Example 8:
Half-life period of \({ }^{14} \mathrm{C}\) is 5760 years. An old piece of wood have a disintegration rate which is 25% of the disintegration rate of an equal weight of a new piece of wood?
Answer:
Let rate of disintegration of new piece =100
The rate of disintegration of old piece =25