#### Online Mock Tests

#### Chapters

Chapter 2: Current Electricity

Chapter 3: Magnetism and magnetic effects of electric current

Chapter 4: Electromagnetic Induction And Alternating Current

Chapter 5: Electromagnetic waves

Chapter 6: Ray Optics

Chapter 7: Wave Optics

Chapter 8: Dual Nature of Radiation and Matter

Chapter 9: Atomic and Nuclear physics

Chapter 10: Electronics and Communication

Chapter 11: Recent Developments in Physics

## Chapter 9: Atomic and Nuclear physics

### Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Physics Volume 1 and 2 Answers Guide Chapter 9 Atomic and Nuclear physics Evaluation [Pages 189 - 192]

#### Multiple Choice Questions

Suppose an alpha particle accelerated by a potential of V volt is allowed to collide with a nucleus whose atomic number is Z, then the distance of closest approach of alpha particle to the nucleus is ______.

14.4 \[\frac{\text{Z}}{\text{V}}\]Å

14.4 \[\frac{\text{V}}{\text{Z}}\]Å

1.44 \[\frac{\text{Z}}{\text{V}}\]Å

1.44 \[\frac{\text{V}}{\text{Z}}\]Å

In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to ______.

h

`"h"/pi`

`(4"h")/pi`

`(2"h")/pi`

Atomic number of H-like atom with ionization potential 122.4 V for n = 1 is ______.

1

2

3

4

The ratio between the first three orbits of a hydrogen atom is ______.

1 : 2 : 3

2 : 4 : 6

1 : 4 : 9

1 : 3 : 5

The charge of cathode rays is ______.

positive

negative

neutral

not defined

In J.J. Thomson e/m experiment, a beam of electron is replaced by that of muons (particle with same charge as that of electrons but mass 208 times that of electrons). No deflection condition is achieved only if

B is increased by 208 times

B is decreased by 208 times

B is increased by 14.4 times

B is decreased by 14.4 times

The ratio of the wavelengths for the transition from n =2 to n = 1 in Li^{++}, He^{+} and H is ______.

1 : 2 : 3

1 : 4 : 9

3 : 2 : 1

4 : 9 : 36

The electric potential between a proton and an electron is given by V = V_{0} In `("r"/"r"_0)`, where r_{0 }is a constant. Assume that Bohr atom model is applicable to potential, then a variation of radius of n^{th} orbit r_{n} with the principal quantum number n is

`"r"_"n" prop 1/"n"`

r

_{n}∝ n`"r"_"n" prop 1/"n"^2`

r

_{n}∝ n^{2}

If the nuclear radius of ^{27}Al is 3.6 fermi, the approximate unclear radius of ^{64 }Cu is ______.

2.4

1.2

4.8

3.6

The nucleus is approximately spherical in shape. Then the surface area of nucleus having mass number A varies as ______.

A

^{2/3}A

^{4/3}A

^{1/3}A

^{5/3}

The mass of a \[\ce{^7_3Li}\] nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of \[\ce{^7_3Li}\] nucleus is nearly ______.

46 MeV

5.6 MeV

3.9 MeV

23 MeV

M_{p }denotes the mass of the proton and M_{n} denotes mass of a neutron. A given nucleus of binding energy B, contains Z protons and N neutrons. The mass M (N, Z) of the nucleus is given by(where c is the speed of light)

M (N, Z) = NM

_{n}+ ZM_{p}– Bc^{2}M (N, Z) = NM

_{n}+ ZM_{p}+ Bc^{2}M (N, Z) = NM

_{n}+ ZM_{p}– B / c^{2}M (N, Z) = NM

_{n}+ ZM_{p}+ B / c^{2}

A radioactive nucleus (initial mass number A and atomic number Z) emits 2α and 2 positrons. The ratio of a number of neutrons to that of protons in the final nucleus will be ______.

`("A" - "Z" - 4)/("Z" - 2)`

`("A" - "Z" - 2)/("Z" - 6)`

`("A" - "Z" - 4)/("Z" - 6)`

`("A" - "Z" - 12)/("Z" - 4)`

The half-life period of radioactive element A is the same as the mean life time of another radioactive element B. Initially both have the same number of atoms. Then

A and B have the same decay rate initially

A and B decay at the same rate always

B will decay at faster rate than A

A will decay at faster rate than B.

A radiative element has N_{0} number of nuclei at t = 0. The number of nuclei remaining after half of a half-life (that is, at time t = `1/2 "T" _(1/2)`).

`"N"_0/2`

`"N"_0/sqrt2`

`"N"_0/4`

`"N"_0/8`

#### Short answer questions

What are cathode rays?

Write the properties of cathode rays.

Give the results of Rutherford alpha scattering experiment.

Write down the postulates of Bohr atom model.

What is meant by excitation energy?

Define the ionization energy.

Define the ionization potential.

Write down the draw backs of the Bohr atom model.

What is distance of closest approach?

Define impact parameter.

Write a general notation of the nucleus of element X. What each term denotes?

What is isotope? Give an example.

What is isotone? Give an example.

What is isobar? Give an example.

Define atomic mass unit u.

Show that nuclear density is almost constant for nuclei with Z > 10.

What is mass defect?

What is binding energy of a nucleus? Give its expression.

Calculate the energy equivalent of 1 atomic mass unit.

Give the physical meaning of binding energy per nucleon.

What is meant by radioactivity?

Give the symbolic representation of alpha decay, beta decay and gamma emission.

In alpha decay, why the unstable nucleus emits \[\ce{^4_2He}\] nucleus? Why it does not emit four separate nucleons?

What is mean life of nucleus? Give the expression.

What is half-life of nucleus? Give the expression.

What is meant by activity or decay rate? Give its unit.

Define curie.

What are the constituent particles of neutron and proton?

#### Long answer questions

Explain the J. J. Thomson experiment to determine the specific charge of an electron.

Discuss the Millikan’s oil drop experiment to determine the charge of an electron.

Derive the energy expression for an eletron is the hydrogen atom using Bohr atom model.

Discuss the spectral series of hydrogen atom.

Explain the variation of average binding energy with the mass number using a graph and discuss about its features.

Explain in detail the nuclear force.

Discuss the alpha decay process with example.

Discuss the beta decay process with examples.

Discuss the gamma decay process with an example.

Obtain the law of radioactivity.

Discuss the properties of neutrino and its role in beta decay.

Explain the idea of carbon dating.

Discuss the process of nuclear fission and its properties.

Discuss the process of nuclear fusion and how energy is generated in stars?

Describe the working of nuclear reactor with a block diagram.

Explain in detail the four fundamental forces in nature.

Briefly explain the elementary particles present in nature.

#### Exercises

Consider two hydrogen atoms H_{A} and H_{B} in ground state. Assume that hydrogen atom H_{A} is at rest and hydrogen atom H_{B} is moving with a speed and make head-on collide on the stationary hydrogen atom H_{A}. After the strike, both of them move together. What is the minimum value of the kinetic energy of the moving hydrogen atom H_{B}, such that any one of the hydrogen atoms reaches one of the excitation state?

In the Bohr atom model, the frequency of transitions is given by the following expression

v = `"Rc" (1/"n"^2 - 1/"m"^2)`, where n < m

Consider the following transitions:

Transitions |
m → n |

1 | 3 → 2 |

2 | 2 → 1 |

3 | 3 → 1 |

Show that the frequency of these transitions obey sum rule (which is known as Ritz combination principle).

- A hydrogen atom is excited by radiation of wavelength 97.5 nm. Find the principal quantum number of the excited state.
- Show that the total number of lines in emission spectrum is `("n"("n - 1"))/2`.

Compute the total number of possible lines in emission spectrum as given in(a).

Calculate the radius of the earth if the density of the earth is equal to the density of the nucleus. [mass of earth 5.97 x 10^{24} kg].

Calculate the mass defect and the binding energy per nucleon of the \[\ce{^108_47Ag}\] nucleus. [atomic mass of Ag = 107.905949].

Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes respectively. Initially, the samples have equal number of nuclei. Calculate the ratio of decayed numbers of A and B nuclei after 80 minutes.

On your birthday, you measure the activity of the sample 210Bi which has a half-life of 5.01 days. The initial activity that you measure is 1µCi.

- What is the approximate activity of the sample on your next birthday? Calculate
- the decay constant
- the mean life
- initial number of atoms.

Calculate the time required for 60% of a sample of radon to undergo decay. Given T_{1/2} of radon = 3.8 days.

Assuming that energy released by the fission of a single \[\ce{^235_92U}\] nucleus is 200MeV, calculate the number of fissions per second required to produce 1-watt power.

Show that the mass of radium \[\ce{^226_88Ra}\] with an activity of 1 curie is almost a gram. Given T1/2 = 1600 years.

Characol pieces of tree is found from an archeological site. The carbon-14 content of this characol is only 17.5% that of equivalent sample of carbon from a living tree. What is the age of tree?

## Chapter 9: Atomic and Nuclear physics

## Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Physics Volume 1 and 2 Answers Guide chapter 9 - Atomic and Nuclear physics

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Concepts covered in Class 12th Physics Volume 1 and 2 Answers Guide chapter 9 Atomic and Nuclear physics are Nuclei, Nuclear Force, Radioactivity, Nuclear Fission, Nuclear Fusion – Energy Generation in Stars, Introduction to Atomic and Nuclear Physics, Electric Discharge Through Gases, Introduction to Atom Models.

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