WBBSE Solutions For Class 10 Physical Science And Environment Chapter 7 Atomic Nucleus

Class 10 Physical Science Solutions WBBSE

Chapter 7 Atomic Nucleus MCQs

Question 1. Which of the following are α-emitter?

1. Helium-5
2. Polonium-212
3. Tritium

Answer: 2. Polonium-212

Question 2. Control rods of nuclear reactors are made up of:

1. Cd
2. Diamond
3. Graphite
4. Copper

Answer: 1. Cd

Question 3. The moderator used in atomic pile is :

1. Heavy water
2. Uranium
3. Iron

Answer:  1. Heavy water

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Question 4. Which one of the following is not a synthetic element?

1. Np
2. Cm
3. PU
4. U

Answer:  4. U

Class 10 Physical Science Solutions WBBSE

Question 5. Which emits b-particle?

1. ₁H³
2. ₆ C¹⁴
3. ₁₉ K⁴⁰
4. All of these.

Answer:  4. All of these.

Question 6. Choose the element which is not radioactive :

1. Cm
2. NO
3. Mo
4. Md

Answer: 3. Mo

Question 7.  ₁H¹ + ₁H³ + ₁H⁴ represents:

1. β-decay
2. Fusion
3. Fussion
4. D-decay

Answer: 2. Fusion.

Question 8. What is the order of reaction of the decay of ₉₂ U²³⁵ ?

1. Zero
2. First
3. Second
4. Third

Answer: 2. First.

Question 9. Which of the following has the maximum ratio?

1. ¹⁶Ne
2. ¹⁶F
3. ¹⁶O
4. ¹⁶N

Answer: 4.¹⁶N

Question 10. Which of the following radioactive elements is soluble in water?

1. Radium
2. Tritium
3. Radon

Answer: 3. Radon.

Question 11. The relative penetrating power of a,ß,y and neutron (n) follows the order:

1. α > β > γ> n
2. n > γ > β >α
3. β >α > n > γ
4. None of these

Answer: 2. n > γ > B > α.

Class 10 Physical Science Solutions WBBSE

Question 12. Which of the following nuclear reactions will generate an isotope?

1. Newtron particle emission
2. Positron emission
3. β – particle emission
4. α – particle emission

Answer: 1. Newtron particle emission.

Question 13. Nuclear energy is :

1. Renewable
2. Not renewable
3. Sometimes renewable
4. It is a matter of debate

Answer: 2. Not renewable.

Question 14. Nuclear fission is initiated by:

1. Slow neutron
2. By proton
3. Fast newtron
4. By α Particle

Answer: 1. Slow neutron.

Question 15. The source of energy of the sun is :

1. Fission reaction.
2. Fusion reaction
3. Spalation reaction
4. None of these

Answer: 2. Fusion reaction.

Question 16. Near the nuclear reactor, there is:

1. Large neutron flux
2. Large proton flux
3. Large Particles flux
4. Large β – ray flux

Answer: 1. Large neutron flux

WBBSE Class 10 Physical Science Question Answer In English

Question 17. A decrease in atomic number is not observed during :

1. α-emission
2. β-emission
3. Positron
4. Electron capture

Answer: ????

Question 18. Identify the nuclear reaction that differs from the rest :

1. Positron emission
2. K-capture
3. γ-decay
4. β-decay

Answer:  3. γ- decay.

Question 19. Which of the following are β-emitters?

1. Carbon-14
2. Cobalt-60
3. Tritium-3
4. All of these

Answer: 4. All of these.

Question 20. Which of the following has the highest value for its radioactivity?

1. 1g of Ra
2. Ig of Ras 04
3. 1g of RaBr₂
4. None of these

Answer: 1. Ig of Ra.

Question 21. Of the following which is not used as a moderator in a nuclear reactor?

1. Heavy water
2. Sodium
3. Graphite

Answer: 2. Sodium.

Question 22. Control rods used in the nuclear reactor are made of:

1. Nickel
2. Iron
3. Graphite
4. Cadmium

Answer: 4. Cadmium.

WBBSE Class 10 Physical Science Question Answer In English

Question 23. Which of the following processes causes the emission of an X-ray?

1. Alpha emission
2. Gamma Emission
3. Electron emission
4. Positron Emission

Answer: 3. Electron emission.

Question 24. Choose the incorrect one:

1. 1 curie = 3.7 × 1010 ds^-1
2. 1 rutherford = 10⁶ ds^-1
3. 1 fermi = 10³ ds-1
4. I becquerel = 1 ds-1

Answer: 3. fermi = 10³ ds^-1

Question 25. Mark the correct relation :

1. No = Ne^tt
2. t= 1.44+0.5
3. N= No(½)^x
4. To.5 = λln²

Answer: 4. To.5 = λln²

Question 26. Choose the natural element among the following:

1. Uranium
2. Astatine
3. Neptunium

Answer: 1. Uranium.

Question 27. α-ray consists of a stream of

1. H^–
2. He^-2
3. Only electrons
4. Only Neutrons

Answer: 2. He^-2

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Question 28. Which of the following combinations will give the most stable nuclear?

1. Odd Z and odd N
2. Odd Z and even N
3. Even Z and odd N
4. Even Z and even N

Answer: 4. Even Z and even N.

Question 29. Emission of a ẞ particle by an atom of element results in the formation of its 

1. Iso tope
2. Isomer
3. Isobar
4. Isomorph

Answer: 3. Isobar.

Question 30. Stable nuclides cannot be obtained for

1. Z = 43, N = 35
2. Z = 61, Z = 89
3. A > 209
4. All of these

Answer:  4. All of these.

Question 31. Which of the following nuclei are stable?

1. ₂₈ Ni⁶⁰
2. ₆ C¹¹
3. ₉₂ U²³³
4. ₄ Be⁸

Answer: 4. ₄ Be⁸

Question 32. Which of the following nuclei is unstable?

1. ₅B¹⁰
2. ₇N¹⁴
3. ₈O¹⁶
4. ₄Be¹⁰

Answer: 4. ₄ Be¹⁰

WBBSE Class 10 Physical Science Solutions

Question 33. A device used for the measurement of radioactivity is 

1. Mass spectrometer
2. Cyclotron
3. G-M-Counter
4. Nuclear reactor

Answer: 3. G-M-Counter.

Question 34. Which of the following radiations, the one most easily stopped by air is 

1. X-rays
2. α-rays
3. β-rays
4. γ -rays

Answer: 1. X-rays.

Question 35. y -Ray:

1. Consist of particles that have mass
2. Are energy waves.
3. Have mass
4. Are deflected by an electric field

Answer: 2. Are energy waves.

Question 36. Loss of B-particle is equivalent to 

1. Increase of one proton
2. Decrease of one neutron
3. Combination of (1) and 2)
4. None of the above

Answer: 3. Combination of  (1)and (2)

Question 37. Which of the following is the man-made radio-active disintegration series?

1. Thorium series
2. Actinium series
3. Uranium series
4. Neptunium series

Answer: 4. Neptunium series.

WBBSE Class 10 Physical Science Solutions

38. Question  ₁₃A²⁷ is a stable isotope. It is expected to disintegrate by 

1. α-emission
2. β – emission
3. β^–– emission
4. Proton emission

Answer: 3. β^–-emission.

Question  39. Positron has a mass equal to 

1. Electron
2. α – particle
3. Proton
4. Deuteron

Answer: 1. Electron.

Question  40. Which of the following has a magic number of protons and neutrons?

1. ₈O¹⁷
2. ₁₃Al²⁷
3. ₉Fl¹⁷
4. ₂₀Ca⁴⁰

Answer: 4. ₂₀Ca⁴⁰

WBBSE Class 10 Physical Science Solutions Chapter 7 Atomic Nucleus Very Short Answer Type Questions

Question 1. Out of αβ and y rays which one is called hand rays?
Answer: γ rays.

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

Question 3. What is the value of the packing fraction for unstable nuclides?
Answer: Positive.

Question 4. What is the value of the packing fraction for stable nuclides?
Answer: Zero or negative.

Question 5. Do nuclear forces obey inverse square law?
Answer: Nuclear forces are not governed by inverse square law

Question 6. Out of a, ẞ and y rays which one causes maximum damage to the body tissues?
Answer: α-rays.

Question 7. What is the density of the nucleus?
Answer: 10¹⁴/ Cm³

Question 8. What is the binding energy for a mass defect of 1 amu?
Answer: 931 5 Mev.

Question 9. What is the n/p ratio of lighter nuclides (Zup to 20)?
Answer: 1.

Question 10. What is the n/p ratio of ₁ft¹ ?
Answer: 0.

Question 11. What is the lifespan of a radioactive element?
Answer: The life span of a radioactive element is infinite.

Question 12. How many a and b particles are emitted from uranium series?
Answer: The uranium series emits 8α and 6β particles.

Question 13. What is artificial series?
Answer: (4n+1) is artificial series.

Question 14. What is the end product of the 4n series?
Answer: The end product of the 4n series is lead.

Question 15. Is the half-life of a radioactive element dependent on its physical and chemical state?
Answer: The half-life of a radioactive element is independent of its physical and chemical state.

Question 16. How mass defects can be converted into energy?
Answer: The mass defect can be converted into energy by using Einstein’s equation ΔE = mc²

WB Class 10 Physical Science Question Answer

Question 17. Write an example of nuclear fission.
Answer:

₉₂ U ²³⁵+ ₀ n¹ → ₃₅ Br ⁸⁷ +₅₇ La¹⁴⁶ + 3 ₀ n¹

Question 18. Write an example of an isotope of carbon.
Answer: An example of an isotope of carbon C- 14.

Question 19. What is the value of the velocity of ẞ Particle?
Answer: The velocity of β particle is maybe up to \(\frac{9}{10}\) the velocity of light.

Question 20. Define.-Helions.
Answer: α particles are He^– ions or bare helium nuclei sometimes called helions.

WB Class 10 Physical Science Question Answer Chapter 7 Atomic Nucleus Fill In The Blanks

Question 1. Radioactivity was proposed by_________
Answer: Madam Curie.

Question 2. Measurement of radioactivity is done by _________
Answer: Geiger-Muller counter.

Question 3. The process of transforming one element into another is known as _________
Answer: Alchemy

Question 4. NO₂ and CO₂, are the examples of _________
Answer: Isosteres

Question 5. The density of the nucleus is of the order of_________
Answer: 10¹⁴

Question 6. Magic numbers are 2, 8, 20, 50, 82 and _________
Answer: 126

Question 7. The difference between the total mass of the particles present in the nucleus of a nuclide and its real mass is called _________
Answer: Mass defect

Question 8. Due to the large mass, α particles possess large _________
Answer: Kinetic energy

Question 9. β-particles are _________ charged
Answer: Negatively

Question 10. γ rays are _________
Answer: Neutral

Question 11. γ-rays have the least effect on _________
Answer: Photographic plates.

Question 12. Isotopes of the same element possess the same number of _________
Answer: Protons.

Question 13. ₁H²+ ₁H³ → ₂He⁴  is a  _________ reaction.
Answer: Fusion.

Question 14. The speed of y-rays is _________ speed of light reaction.
Answer: Equal to

Question 15. The atom bomb is based on nuclear _________ reaction.
Answer: Fission.

Question 16. A hydrogen bomb is based on nuclear _________ reaction.
Answer: Fusion.

Question 17. The source of the energy of the Sun is _________
Answer: Fusion.

Question 18. The number of neutrons in a radioactive isotope of hydrogen is _________
Answer: 2.

Question 19. The rate of disintegration of the active nucleus is known as _________
Answer: Activity.

Question 20. ₇N¹⁴+₀n→ a ____________ + ₇H¹⁴
Answer: ₆C¹⁴

Question 21. The energy equivalent to 1 amu is _________ me V.
Answer: 931.5.

Question 22. The time taken for the decay of half the initial amount of a radioactive nuclide is called _________.
Answer: Half-life period.

Question 23. The phenomenon of spontaneous emission of invisible radiation is called _________.
Answer: Radioactivity.

Question 24. B-particles are nothing but _________ moving at high speeds.
Answer: Electrons.

Question 25. The phenomenon in which a stable nuclide is converted artificially into a radioactive substance is called _________.
Answer: Artificial radioactivity.

Question 26. Isotones are the nuclides having the same number of_________.
Answer: Neutrons.

Question 27. Atoms of the different elements possessing the same mass number are called _________.
Answer: Isobars.

Question 28. According to Einstein’s equation, the relation between mass and energy can be written as  _________.
Answer: E = mc²

Question 29. _________ is α- a-emitter.

Answer: Polonium-212.

Question 30. Positron has a mass equal to _________.
Answer: Electron.

WBBSE Class 10 Physical Science Solutions Chapter 7 Atomic Nucleus Short Answer Type Questions

Question 1. What do you mean by nuclear forces?
Answer:

Nuclear forces: The forces which held the nuclear together within the small nucleus are called nuclear forces.

These forces exist among P-P, P-n and n-n

Question 2. What are nuclear reactions?
Answer:

Nuclear reactions: Nuclear reactions are the reaction in which the nuclear of an atom undergoes a change.

Question 3. What is packing fraction?
Answer: ‘

Packing fraction: Packing fraction was proposed by Aston and defined as the difference between actual isotopic mass and the mass number.

Question 4. What are nuclear isomers?
Answer:

Nuclear isomers: Nuclear species having the same atomic number and same mass number but different radioactive properties are called nuclear isomers.

Examples: ⁶⁹Zn (7½ 13.8 hours) and ⁶⁹Zn (7½, = 57 minute)

Question 5. What is Natural transmutation?
Answer:

Natural transmutation: It is a process in which elements such as radium undergo transmutation on their own.

Question 6. What do you mean by ‘Group Displacement Law?
Answer:

Group Displacement Law:

We know that an a-emission decreases the atomic number of the parent by 2 and P-emission increases the atomic number by 1.

Thus ‘In an a-emission, the parent element will be displaced to a group two places to the left and in ẞ-emission, it will be displaced to a group one place to the right.’

Question 7. What is a spallation reaction?
Answer:

Spallation reaction: High-speed projectiles with energies of approximately 40M V may chip fragments from a heavy nucleus, leaving a small nucleus. This type of reaction is called spallation.

Examples: ₉₂ U ²³⁵+ ₀ n¹ → ₇₄W¹⁸⁷ + 20 ₁H¹+ 35₀ n¹

Question 8. 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: ₉₂ U ²³⁸+₂H⁴ → ₉₂ U ²³⁹+ γ

Question 9. What is the disintegration series?
Answer:

Disintegration series: The whole series of elements starting with the parent radioactive element to the stable end product is called a radioactive disintegration series.

These series are- 4n (4n+1), (4n+2) and (4n+3)

Question 10. What do you mean by ‘Alchemy’?
Answer:

Alchemy: The process of transforming one element into another is known as Alchemy and the person involved in such experiments is called an alchemist.

Question 11. What is a disaster?
Answer:

Isoster: Molecules or ions with the same number of atoms and also the same number of electrons are said to form an isosteric group or more simple isosteres.

Examples: NO₂ and CO₂

Question 12. What is Radioactivity?
Answer:

Radioactivity: It is a process in which the nucleus of certain elements undergo spontaneous disintegration without excitation by any external me

WBBSE Class 10 Physical Science Solutions

Question 13. What do you mean ny ‘isotopes’?
Answer:

Isotopes: The atoms of an element having the same atomic number but different mass numbers are called isotopes.

Examples: ₁H¹,₁H²,₁H³

Question 14. What is Nuclear fission?
Answer:

Nuclear fission: The process of artificial transmutation in which a heavy nucleus is broken down into two lighter nuclei of nearly comparable masses with the release of a large amount of energy is termed nuclear fission.

Examples: ₉₂ U ²³⁵+ ₀ n¹ →₅₆Ba¹⁴⁰+ ₃₆Kr⁹³+ 3 ₀ n¹

Question 15. What is a half-life period?
Answer:

Half-life period: The half-life period of a radioactive isotope is the time required for one-half of the isotope to decay.

⇒ \(t \frac{1}{2}=\frac{0.693}{\lambda}\)

(λ = Disintegration constant)

Question 16. What is nuclear fusion?
Answer:

Nuclear fusion: A nuclear reaction in which two lighter nuclei are fused together to form a heavier nucleus is called nuclear fusion. 2. 3 4

Examples:  ₁H² + ₁H³ → ₂He⁴ +17.6MeV

Question 17. What is Artificial radioactivity?
Answer:

Artificial radioactivity: It is the phenomenon in which the artificial transmutation of a stable nucleus leads to the formation of a radioactive nuclide.

Question 18. What do you mean by ‘Rutherford’?
Answer:

Rutherford: If a radioactive substance has 106 disintegrations per second, it is said to have an activity of one Rutherford.

Question 19. What are magic numbers?
Answer:

Magic numbers: Magic numbers are the numbers 2, 8, 20, 50, 82 and 126. Nuclides having a magic number of either protons or neutrons or both are more stable.

Question 20. What is Radioactive equilibrium?
Answer:

Radioactive equilibrium: Radioactive change being an irreversible process shows equilibrium when a daughter element disinter grates at the same rate at which it is formed from the parent element.

Question 21. What is the packing fraction of
Answer: Packing fraction (isotopic mass-mass number) mass number

Packing fraction= \(\frac{(\text { isotopic mass }- \text { mass number })}{\text { mass number }} \times 10^4\)

= \(\frac{55.92066-56}{560} \times 10^4\)

= – 14.167

So, the packing fraction of ₂₆Fe⁵⁶ is  -14.167

Class 10 Physical Science WBBSE Question 22. How many a and ẞ particles will be emitted by ₈₄ Ra²¹⁸ in changing to ₈₂ pb²⁰⁶?
Answer:

Let x and y be the number of a and ẞ particles involved in bringing about the change

_{⇒ 84} Ra²¹⁸ → ₈₂ pb²⁰⁶ +x ₂He⁴+y _-1e⁰

Comparing the mass number =  218

= 206 + 4x + 0y

⇒ 4x = 12

⇒ x = \(\frac{12}{4}\)

⇒ x= 3

Comparing the atomic numbers

84 = 82 + 2x + y

2x – y = 2

y = 2(3)- 2

y = 6- 2

y = 4

The number of a and ẞ particles emitted in the given nuclear reaction is 3 and 4.

Question 23. Calculate the number of neutrons in the remaining atom after the emission of a particle from the ₉₂ U ²³⁸ atom.
Answer:

On emission of an a-particles atomic mass

If daughter element 238 – 4 = 234 (Mass)

Atomic number of daughter element = 92-2 = 90

Number of Neutrons =Atomic mass – Atomic number 234  – 90=  144.

Question 24. Short Note-y rays.
Answer:

γ rays: γ rays are high-energy electromagnetic waves. This can be shown by diffraction experiments. The penetration power of the y-rays is 10,000. There is no rest mase of γ -rays.

Class 10 Physical Science WBBSE

Question 25. Write four characteristics of γ-rays.
Answer:

1. The mass of y ray is none
2. The nature of y-ray is electromagnetic waves
3. The relative ionisation capacity of γ-rays is 1.
4. The penetration power of γ-ray is 10,000.

Question 26. Short Note-a Gaiger Miller counter.
Answer:

Geiger Miller counter:

Particles produce scintillations on Zns screens and can easily be detected. One can detect and count the number of β -Particles with the help of the Geiger Muller counter. It consists of a tube fitted with two electrodes at the two ends and contains an inert gas like neon or argon.

Question 27. Short Note β -particles.
Answer:

β -Particles: By measuring the e/m of the B-particles by deflecting them in the an-electric field and a magnetic field it has been conclusively proved that the β – particles are nothing but high-speed electrons. In artificial radioactivity, however, β – particles can be emitted as positrons also.

Question 28. Short Notes a-particle.
Answer:

α-particles = α-particles are in fact. The ions or bare helium nuclei are sometimes called helions. That the a-particles are He^– can be easily proved in a laboratory, acquire squirt electrons from the surrounding and get neutralised to produce helium atoms. The spectrum of the gas obtained from the a-particles emitted from a radioactive source confirms this point.

As α-particles are neutralised to give helium atoms, uranium mines are always found to be a very good source of helium gas. One can early count the number of particles emitted by a radioactive source, in a given time from the scintillation in an Instrument called Spintharis cope.

It is from the ionisation in a Gelger-Muller counter. One can also measure the amount of positive charge imparted to a metal plate during the same period, one can now determine the number of units of charge each particle carries by dividing the total charge imparted to the metal by the total number of particles emitted during the period. It is found to be two units (taking the amount of electronic charge as a unit). ]

Question 29. Radioactivity is a nuclear phenomenon Explain it.
Answer:

If we take two compounds of a radioactivity element containing the same amount of the element, the measured amounts of radioactivity in the two cases appear to be the same in both cases.

This fact shows that radioactivity is a property of an element, not of a compound. While discussing the cause of radioactivity Rutherford and Soddy commented that radioactivity was an unclear phenomenon.

They presented the following arguments in flavour of Heir’s view. When an atom of radioactive element emits a particle the element loses its atomic mass by 4 units and is converted into an atom written the Uranum series of radioactive elements.

Question 30. Write four characteristics of -rays.
Answer:

1. The nature of β – rays is electrons
2. The mass of β- the ray is \(\frac{1}{1856}\) AMU.
3. The relative ionisation Capacity is 100
4. The penetration power is 100.

Question 31. Short Note-Soddy Fajan’s rule.
Answer:

Soddy Fajan’s Rule:

A problem arose about the placement of the elements of the Uranium series in the periodic table soon after their discovery. It was observed that the element formed by the emission of a particle followed by the emission of two β – particles starting from U, with the atomic mass and atomic number producing an element which had the same chemical properties as that of U.

Question 32. Establish the equation of the rate of radioactive disintegration for a half-life period.
Answer:

We know \(\frac{\mathrm{dN}}{\mathrm{dt}}\) α N

\(\frac{\mathrm{dN}}{\mathrm{dt}}\) = λN ______ (1)

λ = Radioactive disintegration

Integrating the equation  (1)

N= Noe – λ^t______ (2)

Taking Lagarithm and simplification

λ = \(\lambda\frac{1}{7} \ln \frac{\mathrm{No}}{\mathrm{N}}=\frac{2.303}{7} \log \frac{\mathrm{No}}{\mathrm{N}}\)

λ =  \(\frac{1}{\frac{t_{01}}{2}} \ln _2=\frac{2.203}{\frac{t_1}{2}} \log 2=\frac{0.693}{t_{\frac{1}{2}}}\)

λ =  \(\mathrm{t}_{\frac{1}{2}}=\frac{0.693}{\lambda}\)

Class 10 Physical Science WBBSE

Question 33. What is the integration form of the rate of radioactive disintegration?
Answer:

We know, \(\frac{\mathrm{dN}}{\mathrm{dt}}\) α N

\(\frac{\mathrm{dN}}{\mathrm{dt}}\)α N

\(\frac{\mathrm{dN}}{\mathrm{dt}}\) = λn

λ = Radioactive disintegration

Integrating the equation, N Noe – λ^t

No initial number of atoms of the radioactive element.

Question 34. Define isotope. Write an example of the isotope.
Answer:

Isotope Some elements have the same atomic numbers though they have different numbers. They are called isotopes as they occupy the same position in the periodic table.

Example: ₉₂U²³⁸

Question 35. Write about the rate of radioactive disintegration.
Answer: If there are N number of atoms of a radioactive element in a sample at a

The particular instant of time, the rate of disintegration at that instant will be proportion to N.

\(\frac{\mathrm{dN}}{\mathrm{dt}}\)α N

\(\frac{\mathrm{dN}}{\mathrm{dt}}\)= – λN

γ = Constant (radioactive disintegration).

Chapter 7 Atomic Nucleus Broad Answer Type Questions

Question Explain the separation of isotopes through the diffusion method.
Answer:

Though the isotopes have identical chemical properties, some of their physical properties may be quite different because of the difference in their mass numbers.

The most important physical properties of this type are the rate of diffusion, boiling point, and radioactive properties isotopes of elements can be separated by physical methods based on their properties. They may be separated almost completely using a special type of instrument called the mass spectrometer.

Diffusion method:

Since the rate of diffusion of a gas varies inversely to the square root of its molecular mass. Gas molecules with lower atomic mass numbers diffuse more quickly than their heavier sisters.

This principle was very effected actively used by Aston for the separation of isotopes of neon. The more is the difference in the atomic mass numbers, the more effective is the separation.

Class 10 Physical Science WBBSE

Question 2. Write the cause of radioactivity.
Answer:

Cause of radioactivity:

The main reason for the radioactivity of an element, as we have noted earlier, is the instability of its nucleus. Such an unstable nucleus tries to attain stability through the expulsion of particles and rays. If there are too many protons in a nucleus they will fall apart and the element will disintegrate. Again, it the nucleus is too heavy with too many neutrons it disintegrates.

It is observed that in order to attain stability the neutron: Proton ratio must be mear about unity for the elements with low atomic masses while for the heavier elements, it must not exceed 1.5.

Thus we see that most of the radioactive elements have very high atomic masses in ₉₂U²³⁴ in comparison to their atomic numbers U has a neutron; proton ratio of 1.537 while radium has 1.56. This is why radium is much more radioactive than uranium.

Question 3. Short Note-Radioactive Equilibrium.
Answer:

Radioactive Equilibrium :

The product element formed by the radioactive disintegration of an element may also be radioactive. The process goes an until the chain is terminated by the birth of a non-radioactive stable element at the end of a series. If we keep a sample of a radioactive element or its salt for a sufficient time, a situation arises when the rate of creation and the rate of disintegration of a product element become equal.

This state for a radioactive series is called a radioactive equilibrium. We see that at the equilibrium.

⇒ \(\frac{\mathrm{dN}_1}{\mathrm{dt}}=\frac{\mathrm{dN}_2}{\mathrm{dt}}=\frac{\mathrm{dN}_3}{\mathrm{dt}}\)

∴ λ₁ N₁ = λ₂ N₂ = λ₃ N₃ = …………

Question 4. Short Note Mass spectrometric method to separate the isotope.
Answer:

Mass spectrometric method:

In this method positive particles of the required gas or vapour formed by bombardment with electrons are first passed through electrical plates with a potential difference (X) of about 1000 volts and two collimating slits. The electrical energy Xe, where e is the charge of the positive particles, is equal to the kinetic energy of the particles.

That is Xe =½ mu² where m and v are the mass and the charge of the positive particles. The positive particles energing through a slit with almost equal kinetic energy pass a magnetic field (H) between two semicircular.

Question 5. What is binding energy? Short Note-Stability of an atomic nucleus packing fraction.
Answer:

The amount of energy that can be obtained by the amount of mass equal to the mass defect is known as the binding energy.

1. The atomic mass of an isotope of an element is expected to be equal to the Sun of the fundamental particles present in it. In AMU the mass of a proton or a neutron is nearly equal to unity while that of an electron is negligible.
2. Atomic masses of isotopes of elements are expected to be approximately whole numbers. Called atomic mass numbers.

Packing faction =  \(\frac{\text { Actual mass of a nucleus }- \text { Mass number }}{\text { Mass number }} \times 10^4\)

WB Class 10 Physical Science Question Answer

Question 6. What are isotones? Define-nuclear isomers.
Answer:

The are elements which differ in both their atomic numbers as well as most numbers but they have the same number of neutrons in their nuclei. They are called isotones.

The two nuclei of an element may have the same atomic number and the same mass number yet differ in their internal nuclear energies. These nuclei are called nuclear isomers.

Question 7. Explain the separation of isotopes by distillation under low pressure.
Answer:

Distillation under low pressure: When a liquid like mercury is distilled under low pressure the lighter isotopes come out more quickly and condense on a cooler surface. The condensate is collected, melted and subjected to the same procedure. B repeating the process the condensate can be made richer in the lighter variety.

Question 8.  What do you mean by isobars and isotones?
Answer: Isobars The nuclide of different chemical elements having the same mass number but different atomic numbers are called isobars.

Examples:

1. ₁₈ Ar⁴⁰
2. ₁₉K⁴⁰
3. ₂₀Ca⁴⁰

Isotones: The nuclides of different chemical elements having the same number of neutrons but different atomic numbers are called isotones.’

Examples: ₁H³, ₂He⁴

Question 9. What are the parent and end products of different disintegration series?
Answer: Series

Question 10. What are the differences between nuclear fission and nuclear fusion?
Answer:

Difference between nuclear fission and nuclear fusion :

Question 11. What do you mean by Curie and Becquerel?
Answer:

• Curie If a radioactive substance disintegrates at the rate of 3.7 × 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 Be equal.

WB Class 10 Physical Science Question Answer

Question 12. A radioactive substance decays at such a rate that after 46 days only 0.25 of its original amount is left to calculate its disintegration constant.
Answer:

Let, the original amount be No then Amount after 46 days, Nt = 0.25 x No For a nuclear decay,

λ = \(\frac{2.303}{\mathrm{t}} \log \frac{\mathrm{No}}{\mathrm{Nt}}\)

= \(\frac{2.303}{46}\) log⁴ day^-1

= 0.0301day^-1

Question 13. A certain nuclide has a half-life of 60 min. If a sample containing 600 atoms is allowed to decay for 90 min, what will be the remaining atoms?
Answer:

λ = \(\frac{0.693}{60} \mathrm{~min}^{-1}\)

= \(\frac{2.30^3}{90} \log \frac{\mathrm{No}}{\mathrm{N}}\)

⇒ log \(\frac{\mathrm{No}}{\mathrm{N}}\) = 0.4514 Or,

⇒ log \(\frac{\mathrm{No}}{\mathrm{N}}\)= 2.828

∴N = \(\frac{600}{2.823}\)

N= 212

Question 14. The activity of a sample of radioactive element A100 is 6.02 curie. Its decay constant is 3.7 x 10’S’ which calculates the initial mass of the sample.
Answer:

Activity = \(\lambda \times \frac{\mathrm{wt}}{\text { at. wt }} \times 6.023 \times 10^{23}\)

\(6.02 \times 3.7 \times 10^{10}=3.7 \times 10^4 \times \frac{w}{100} \times 6.023 \times 10^{23}\)

 

W= \(\frac{6.02 \times 3.7 \times 10^{10} \times 100}{3.7 \times 1.04 \times 6.023 \times 10^{23}}\)

W= \(10^{-15} \mathrm{~g}\)

Question 15. The half-life period of C is 5760 years. An old piece of wood has a disintegration rate which is 25% of the disintegration rate of an equal weight of a new piece of wood.
Answer: Let the rate of disintegration of the new piece = 100

The rate of migration of old pieces = 25

K = \(\frac{0.693}{\frac{t_1}{2}}=\frac{0.693}{5760}\)

t= \(\frac{2.303}{K} \log \frac{a}{a-x}\)

=\(\frac{2.303}{K} \log \left(\frac{\mathrm{lo}}{\mathrm{It}}\right)\)

∴ \(=\frac{2.30 \times 5760}{0.693} \log \frac{100}{25}\)

t= 11523 years.