B.Sc. T.Y. Sem-VI Paper:Atomic And Molecular Physics (Test Paper)

Molecular spectroscopy is the study of how molecules interact with electromagnetic radiation. It is used in various applications, including structural investigation, understanding colors, and studying energetically excited reaction products. In structural investigation, molecular spectroscopy helps determine the arrangement and bonding of atoms within a molecule. Understanding colors involves studying the absorption and emission of light by molecules. Lastly, molecular spectroscopy is used to analyze the products of reactions that involve the transfer of energy. Therefore, all of the mentioned options are applications of molecular spectroscopy.

Fusion reactions are called thermonuclear because they involve the combination of atomic nuclei at extremely high temperatures, typically millions of degrees Celsius. These high temperatures are necessary to overcome the electrostatic repulsion between positively charged nuclei and allow them to come close enough for the strong nuclear force to bind them together. The term "thermonuclear" combines "thermo," meaning heat, with "nuclear," referring to the atomic nuclei involved in the reaction.

One atomic mass unit (AMU) is equal to 1.66 x 10^-24 g. This is because an atomic mass unit is a unit of mass used to express atomic and molecular weights. It is defined as 1/12th the mass of a carbon-12 atom, which is approximately 1.66 x 10^-24 grams.

Neutrons are bombarded on heavy nuclei of nuclear fuel. This is because neutrons are uncharged particles and can easily penetrate the positive charge of the nucleus without being repelled. When neutrons collide with heavy nuclei, they can initiate nuclear reactions such as fission or fusion, which release large amounts of energy. This is the basis of nuclear power and nuclear weapons. Electrons, protons, and photons are not typically used for bombarding heavy nuclei in nuclear reactions.

U238 is the most abundant isotope of uranium on Earth. Isotopes are atoms of the same element with different numbers of neutrons in their nucleus. U238 has 92 protons and 146 neutrons, making it the most common isotope of uranium. It is found in large quantities in the Earth's crust and is used as a fuel in nuclear reactors. U238 undergoes radioactive decay over time, eventually transforming into other isotopes, including U235, which is also used as a fuel in some reactors.

The splitting of lines into groups under the effect of an electric or magnetic field is known as the Zeeman effect. This phenomenon was discovered by Dutch physicist Pieter Zeeman in 1896. When an atom or molecule is exposed to a magnetic field, the energy levels of its electrons split into multiple sublevels, resulting in the splitting of spectral lines. This effect provided important evidence for the quantization of energy levels in atoms and laid the foundation for the development of quantum mechanics.

The correct answer is "All of the mentioned" because a molecule can possess all three types of energies mentioned. Electronic energy refers to the energy associated with the movement of electrons within the molecule. Vibrational energy refers to the energy associated with the vibration of the molecule's atoms and bonds. Rotational energy refers to the energy associated with the rotation of the molecule around its center of mass. Therefore, all three types of energies can exist simultaneously in a molecule.

Raman effect is the scattering of photons. When light interacts with a molecule or an atom, the energy of the incident photons can be absorbed, re-emitted, or scattered. In the case of Raman scattering, the incident photons interact with the vibrational or rotational modes of the molecules, causing a shift in their energy levels. This shift is then observed as a change in the wavelength or frequency of the scattered photons, providing valuable information about the molecular structure and dynamics.

The splitting of spectral lines due to an electric field is known as the Stark effect. This effect occurs when the energy levels of an atom or molecule are perturbed by an external electric field, causing the spectral lines to split into multiple components. The Stark effect is named after Johannes Stark, who first observed and explained this phenomenon in 1913. It is an important concept in atomic and molecular spectroscopy and has applications in various fields such as astrophysics and plasma physics.

When the center of gravity of a molecule changes during motion, it indicates that the molecule is undergoing translation, which refers to the movement of the entire molecule from one place to another. This type of motion involves the molecule as a whole, rather than any internal vibrations or rotations. Therefore, the molecule possesses translational energy, which is the energy associated with its movement through space.

The quantum number "n" represents the principal quantum number, which determines the energy level or shell that an electron belongs to. It indicates the distance of the electron from the nucleus and the size of the orbital. Therefore, the quantum number "n" gives the shell to which the electron belongs.

The maximum number of electrons in a shell is determined by the formula 2n^2, where n represents the shell number. This formula follows the pattern of the periodic table, where each shell can hold a specific number of electrons. The formula suggests that the first shell (n=1) can hold a maximum of 2 electrons, the second shell (n=2) can hold a maximum of 8 electrons, the third shell (n=3) can hold a maximum of 18 electrons, and so on. Therefore, the correct answer is 2n^2.

The total value of the magnetic quantum number is given by 2l + 1. The magnetic quantum number (m) represents the orientation of the orbital in a magnetic field and can have integer values ranging from -l to +l. The value of l represents the azimuthal quantum number, which determines the shape of the orbital. Therefore, the total value of the magnetic quantum number is obtained by multiplying the range of values for m by 2 and adding 1.

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During the fusion of hydrogen into helium, energy is released. This is because the fusion process involves the conversion of hydrogen nuclei (protons) into helium nuclei, which releases a large amount of energy in the form of light and heat. This energy release is due to the conversion of a small fraction of the mass of the hydrogen nuclei into energy, according to Einstein's famous equation E=mc². Therefore, the correct answer is that energy is released during the fusion of hydrogen into helium.

In nuclear power stations, the nuclear reaction that is performed is nuclear fission. Nuclear fission involves the splitting of a heavy nucleus, such as uranium or plutonium, into smaller fragments, releasing a large amount of energy in the process. This energy is used to generate heat, which is then converted into electricity. Nuclear fusion, on the other hand, involves the merging of light atomic nuclei to form a heavier nucleus, and it is not currently used as a practical energy source in nuclear power stations. Therefore, the correct answer is nuclear fission.

In nuclear fission, each neutron that causes fission releases more than one new neutron. This is because when a nucleus undergoes fission, it splits into two or more smaller nuclei, along with the release of several neutrons. These newly released neutrons can then go on to cause further fission reactions, leading to a chain reaction. Therefore, the number of neutrons released is greater than the number that initially caused the fission.

The correct answer is nuclear fusion. Nuclear fusion is the process in which two or more atomic nuclei come together to form a heavier nucleus, releasing a large amount of energy in the process. This is the reaction that takes place in the sun, where hydrogen nuclei combine to form helium, releasing a tremendous amount of energy in the form of light and heat. Nuclear fission, spontaneous fission, and double beta decay are different types of nuclear reactions, but they do not occur in the sun.

Nuclear fusion is the correct answer because it refers to the process where two light nuclei combine to form a heavier nucleus. This process releases a large amount of energy and is the source of power in stars, including the Sun. In contrast, nuclear fission is the process where a heavy nucleus splits into two or more lighter nuclei, while nuclear power refers to the use of nuclear reactions to generate electricity. Nuclear transmutation, on the other hand, refers to the conversion of one element into another through nuclear reactions.

The correct expression for the orbital angular momentum is [ l (l +1)]1/2. This expression is derived from the quantum mechanical description of angular momentum, where l represents the quantum number associated with the orbital angular momentum. The expression [ l (l +1)]1/2 is used to calculate the magnitude of the orbital angular momentum.

The function of a moderator in a nuclear reactor is to slow down neutrons. Neutrons released during nuclear fission have high energy and need to be slowed down in order to efficiently cause further fission reactions. Graphite and heavy water are commonly used as moderators because they have properties that allow them to interact with neutrons and reduce their kinetic energy. This slowing down of neutrons increases the chances of their absorption by other fuel nuclei, thus sustaining the chain reaction.

EM waves, or electromagnetic waves, can vary in wavelength from meters to nano-meters. Wavelength is the distance between two consecutive peaks or troughs of a wave. The longer the wavelength, the lower the frequency and the lower the energy of the wave. Meters represent longer wavelengths, while nano-meters represent shorter wavelengths. Therefore, the correct answer is "Meters to nano-meters."

The heaviest among the given options is the atom. An atom consists of protons, neutrons, and electrons. While protons and neutrons have similar masses, electrons are much lighter. However, the mass of an atom is not solely determined by the number of its constituents. It also depends on the type and arrangement of atoms in a molecule.

X-rays are a type of electromagnetic radiation that is produced outside the nucleus. Unlike alpha, beta, and gamma radiation, which are all forms of nuclear radiation, X-rays are generated by high-energy electron transitions in atoms. They are commonly used in medical imaging and other applications due to their ability to penetrate materials and create detailed images.

Cadmium rods are used in a nuclear reactor to control its operation. These rods are made of cadmium, which has a high neutron-absorbing capability. By inserting or withdrawing these rods into the reactor core, the amount of neutron flux can be regulated. This control is crucial for maintaining the stability and safety of the nuclear reactor. Therefore, cadmium rods are not used for promoting chain reaction or creating more neutrons, but rather for controlling the operation of the nuclear reactor.

Stars are composed mostly of hydrogen and helium. This is because the process of nuclear fusion that occurs in the core of a star requires high temperatures and pressures, which can only be achieved with light elements like hydrogen and helium. These elements undergo fusion reactions to form heavier elements like iron, but iron is only present in the core of a star and not in significant amounts throughout the entire star. Therefore, the correct answer is that stars are composed of about 3/4 hydrogen and 1/4 helium.

During fission, the original nucleus splits into two smaller nuclei, releasing energy. The mass of the products is equal to the original nucleus because according to the law of conservation of mass, mass cannot be created or destroyed, only transferred or transformed. Therefore, the total mass of the products after fission is equal to the mass of the original nucleus.

When energy is released from a system, it often takes the form of heat or light. According to the principle of mass-energy equivalence (E=mc^2), energy has mass. Therefore, when energy is released, the mass of the system decreases because some of the mass has been converted into energy. This is why the correct answer is "Decreases".

Nuclear binding energy is typically measured in electron volts (eV). The electron volt (eV) is a unit of energy commonly used in atomic and nuclear physics. It represents the amount of kinetic energy gained or lost by a single electron when it moves through an electric potential difference of one volt. Therefore, the correct answer is "ev".

During natural radioactivity, an unstable nucleus undergoes a process called radioactive decay, where it disintegrates and transforms into a more stable state. This decay can occur through various processes such as alpha decay, beta decay, or gamma decay. These processes involve the emission of particles or energy from the nucleus, which helps it reach a more stable configuration. Therefore, the correct answer is "unstable" because a nucleus that undergoes natural radioactivity is initially unstable and seeks to achieve a more stable state.