Question 1
Who discovered the electron?
Correct Answer: J.J. Thomson
Question 2
Thomson's atomic model is commonly known as:
Correct Answer: Plum pudding or watermelon model
Question 3
Which experiment led to the discovery of the atomic nucleus?
Correct Answer: Rutherford's alpha-particle scattering experiment
Question 4
In Rutherford's scattering experiment, most of the alpha particles passed through the gold foil:
Correct Answer: Undeviated (straight through)
Question 5
What is the distance of closest approach (r_0) of an alpha particle of kinetic energy K to a nucleus of atomic number Z?
Correct Answer: r_0 = (1 / 4πε₀) · (2 Z e² / K)
Question 6
What is the main drawback or limitation of Rutherford's atomic model?
Correct Answer: It could not explain the stability of atoms (accelerating electrons should radiate energy and spiral into nucleus)
Question 7
Bohr's quantization condition for angular momentum states that:
Correct Answer: L = m v r = n (h / 2Ï€)
Question 8
The radius of the n-th Bohr orbit in hydrogen atom is proportional to:
Correct Answer: n²
Question 9
What is the radius of the first Bohr orbit (r₁) in a hydrogen atom?
Correct Answer: 0.529 Ã… (5.29 × 10⁻¹¹ m)
Question 10
The velocity of an electron in the n-th Bohr orbit of hydrogen atom varies as:
Correct Answer: 1 / n
Question 11
The total energy of an electron in the n-th Bohr orbit is given by:
Correct Answer: E_n = -13.6 / n² eV
Question 12
What is the ionization energy of hydrogen atom in ground state (n = 1)?
Correct Answer: +13.6 eV
Question 13
Which spectral series of hydrogen atom lies in the ultraviolet region?
Correct Answer: Lyman series
Question 14
Which spectral series of hydrogen atom lies in the visible region?
Correct Answer: Balmer series
Question 15
Which spectral series of hydrogen atom lies entirely in the infrared region?
Correct Answer: Paschen, Brackett, and Pfund series
Question 16
Rydberg formula for wave number (ν̄) of spectral lines is given by:
Correct Answer: ν̄ = R · (1/n₁² - 1/n₂²)
Question 17
What is the approximate value of Rydberg constant (R) for hydrogen?
Correct Answer: 1.097 × 10⁷ m⁻¹
Question 18
What is the potential energy of an electron in the n-th Bohr orbit of hydrogen atom?
Correct Answer: U = -27.2 / n² eV
Question 19
What is the kinetic energy of an electron in the n-th Bohr orbit of hydrogen atom?
Correct Answer: K = +13.6 / n² eV
Question 20
The ratio of kinetic energy to total energy of an electron in a Bohr orbit is:
Correct Answer: -1
Question 21
What is the ratio of potential energy to total energy of an electron in a Bohr orbit?
Correct Answer: +2
Question 22
Who discovered the neutron?
Correct Answer: James Chadwick
Question 23
According to Bohr's model, when an electron jumps from a higher orbit (n₂) to a lower orbit (n₁), the frequency (ν) of emitted photon is:
Correct Answer: hν = E_{n2} - E_{n1}
Question 24
What is the total number of spectral lines emitted when an electron in hydrogen atom drops from 4th excited state (n = 5) to ground state (n = 1)?
Correct Answer: 10
Question 25
What is the radius of the 2nd Bohr orbit (n = 2) in hydrogen atom?
Correct Answer: 2.12 Ã… (or 2.116 × 10⁻¹¹ m)
Question 26
What is the energy of an electron in the 2nd Bohr orbit (n = 2) of hydrogen atom?
Correct Answer: -3.4 eV
Question 27
What is the energy of an electron in the 3rd Bohr orbit (n = 3) of hydrogen atom?
Correct Answer: -1.51 eV
Question 28
What is the energy of an electron in the 4th Bohr orbit (n = 4) of hydrogen atom?
Correct Answer: -0.85 eV
Question 29
What is the frequency of revolution of an electron in the n-th Bohr orbit proportional to?
Correct Answer: 1 / n³
Question 30
Which of the following atoms has only one electron like hydrogen (hydrogen-like ion)?
Correct Answer: He⁺ (Singly ionized helium)
Question 31
For a hydrogen-like ion of atomic number Z, the radius of the n-th Bohr orbit is proportional to:
Correct Answer: n² / Z
Question 32
For a hydrogen-like ion of atomic number Z, the energy of an electron in the n-th orbit is proportional to:
Correct Answer: Z² / n²
Question 33
What is the shortest wavelength present in the Paschen series of hydrogen spectrum?
Correct Answer: 9 / R (or 820 nm)
Question 34
What is the longest wavelength present in the Balmer series of hydrogen spectrum?
Correct Answer: 36 / (5R) (or 6563 Ã… / H-alpha line)
Question 35
What is the shortest wavelength in the Balmer series of hydrogen?
Correct Answer: 4 / R (or 3646 Ã…)
Question 36
Why does an atom emit discrete spectral lines instead of a continuous spectrum?
Correct Answer: Because electrons exist in quantized discrete energy levels
Question 37
What is the impact parameter (b) for an alpha particle heading directly towards the center of the nucleus (head-on collision)?
Correct Answer: Zero
Question 38
What is the scattering angle θ for an alpha particle having impact parameter b = 0 (head-on collision)?
Correct Answer: 180° (rebounds back)
Question 39
What is the scattering angle θ for an alpha particle with a very large impact parameter (b is large)?
Correct Answer: Approximately 0° (passes almost undeviated)
Question 40
What is the angular momentum of an electron in the 3rd Bohr orbit (n = 3)?
Correct Answer: 3h / (2Ï€)
Question 41
What is the minimum excitation energy for a hydrogen atom from ground state (n = 1) to first excited state (n = 2)?
Correct Answer: 10.2 eV
Question 42
What is the excitation energy for transition from n = 1 to n = 3 in hydrogen atom?
Correct Answer: 12.09 eV
Question 43
According to Bohr's postulates, what are stationary orbits?
Correct Answer: Orbits in which electrons do not radiate energy even though they accelerate
Question 44
What is the order of nuclear size (radius R) compared to atomic size?
Correct Answer: Nuclear radius is about 10⁻¹⁵ m (1 fm), whereas atomic radius is about 10⁻¹⁰ m (1 Ã…)
Question 45
What fraction of volume of an atom is occupied by its nucleus roughly?
Correct Answer: About 10⁻¹⁵ of the total atomic volume
Question 46
In Bohr's model, what is the centripetal force on the electron provided by?
Correct Answer: Electrostatic attraction between nucleus and electron
Question 47
What is the frequency of the emitted photon when an electron transitions between two energy levels E₂ and E₁?
Correct Answer: ν = (E₂ - E₁) / h
Question 48
Which series in hydrogen spectrum corresponds to transitions ending at n = 1?
Correct Answer: Lyman series
Question 49
Which series in hydrogen spectrum corresponds to transitions ending at n = 2?
Correct Answer: Balmer series
Question 50
Which series in hydrogen spectrum corresponds to transitions ending at n = 3?
Correct Answer: Paschen series
Question 51
Which series in hydrogen spectrum corresponds to transitions ending at n = 4?
Correct Answer: Brackett series
Question 52
Which series in hydrogen spectrum corresponds to transitions ending at n = 5?
Correct Answer: Pfund series
Question 53
What is the minimum energy required to remove an electron from the ground state of hydrogen atom?
Correct Answer: 13.6 eV
Question 54
What is the angular speed of an electron in the n-th Bohr orbit proportional to?
Correct Answer: 1 / n³
Question 55
What is the magnetic dipole moment associated with an electron revolving in the n-th Bohr orbit proportional to?
Correct Answer: n
Question 56
Bohr magneton (μ_B) is the magnetic moment of an electron in the first Bohr orbit, its value is approximately:
Correct Answer: 9.27 × 10⁻²⁴ J/T (or A·m²)
Question 57
What is the impact parameter for an alpha particle scattering angle of 90°?
Correct Answer: Equal to half the distance of closest approach (r_0 / 2)
Question 58
Why are alpha particles chosen for scattering experiments instead of electrons or protons?
Correct Answer: Because they are heavy and positively charged, carrying enough momentum to probe the nucleus
Question 59
What is an alpha particle fundamentally?
Correct Answer: A doubly ionized helium atom (He²⁺ nucleus containing 2 protons and 2 neutrons)
Question 60
What is the wavelength of the first line of the Balmer series (H-alpha line)?
Correct Answer: 6563 Ã… (656 nm)
Question 61
What is the ground state energy of a doubly ionized lithium ion (Li²⁺, Z = 3)?
Correct Answer: -122.4 eV (-13.6 × 3² eV)
Question 62
What is the ground state energy of a singly ionized helium ion (He⁺, Z = 2)?
Correct Answer: -54.4 eV (-13.6 × 2² eV)
Question 63
Which of the following transitions in hydrogen atom emits a photon of maximum wavelength?
Correct Answer: From n = 3 to n = 2
Question 64
Which of the following transitions in hydrogen atom emits a photon of minimum wavelength (maximum energy)?
Correct Answer: From n = infinity to n = 1 (series limit)
Question 65
What is the main success of Bohr's atomic model?
Correct Answer: It successfully explained the stability of atoms and the line spectra of hydrogen
Question 66
What is the orbital magnetic dipole moment (μ_L) of an electron in the n-th Bohr orbit?
Correct Answer: μ_L = (e / 2m) · L = n (e h / 4Ï€ m)
Question 67
What is the gyromagnetic ratio (ratio of magnetic moment to angular momentum e/2m) for an orbiting electron?
Correct Answer: e / (2 m)
Question 68
Why does the total energy of an electron in a Bohr orbit have a negative sign?
Correct Answer: Because the electron is bound to the nucleus by attractive electrostatic forces
Question 69
What is the speed of an electron in the first Bohr orbit of hydrogen atom as a fraction of speed of light (c)?
Correct Answer: Roughly 1 / 137 of c (fine structure constant)
Question 70
What is the main limitation of Bohr's model when applied to multi-electron atoms (like Helium, Lithium, etc.)?
Correct Answer: It cannot account for electron-electron interactions and complex spectral fine structures
Question 71
What is the angular momentum of an electron in the ground state of hydrogen according to Bohr's theory?
Correct Answer: h / (2Ï€)
Question 72
In Rutherford's model, what trajectory is traced by an alpha particle experiencing a large deflection?
Correct Answer: Hyperbola
Question 73
What is the wavelength of the series limit of Lyman series in hydrogen spectrum?
Correct Answer: 1 / R (or 912 Ã…)
Question 74
What is the series limit wavelength of Balmer series in hydrogen?
Correct Answer: 4 / R (or 3646 Ã…)
Question 75
If an electron jumps from n = 4 to n = 2 in hydrogen, which spectral line is emitted?
Correct Answer: H-beta line of Balmer series
Question 76
What is the radius of nucleus of mass number A proportional to?
Correct Answer: A^(1/3)
Question 77
What is the nuclear density of matter inside a nucleus?
Correct Answer: Approximately constant (independent of mass number A, around 2.3 × 10¹⁷ kg/m³)
Question 78
What is the binding energy per nucleon approximately for stable medium-mass nuclei?
Correct Answer: About 8 MeV per nucleon
Question 79
Which of the following describes nuclear forces?
Correct Answer: Strong, short-range, attractive, and charge-independent force
Question 80
What is mass defect (Δm) of a nucleus containing Z protons and N neutrons with nuclear mass M?
Correct Answer: Δm = [Z m_p + N m_n] - M
Question 81
What is binding energy (BE) in terms of mass defect (Δm)?
Correct Answer: BE = Δm · c²
Question 82
What is nuclear fission?
Correct Answer: Splitting of a heavy nucleus into two smaller nuclei with release of enormous energy
Question 83
What is nuclear fusion?
Correct Answer: Combination of two or more light nuclei to form a heavier nucleus with energy release
Question 84
What is the source of energy in the Sun and stars?
Correct Answer: Nuclear fusion (fusion of hydrogen into helium)
Question 85
What is radioactive decay law formula expressing number of undecayed nuclei N at time t?
Correct Answer: N(t) = N₀ e^(-λt)
Question 86
What is the relation between half-life (T_1/2) and decay constant (λ) of a radioactive substance?
Correct Answer: T_(1/2) = ln(2) / λ ≈ 0.693 / λ
Question 87
What is mean life (τ) of a radioactive substance in terms of decay constant (λ)?
Correct Answer: τ = 1 / λ
Question 88
What is 1 atomic mass unit (1 amu or u) equal to in terms of kg?
Correct Answer: 1.66 × 10⁻²⁷ kg
Question 89
What is the energy equivalent of 1 amu in MeV?
Correct Answer: 931.5 MeV
Question 90
Which radioactive decay involves emission of a helium nucleus (²⁴He)?
Correct Answer: Alpha decay
Question 91
What particle is emitted during beta-minus (β⁻) decay along with the daughter nucleus?
Correct Answer: Electron and an antineutrino
Question 92
What is emitted during gamma (γ) decay from an excited nucleus?
Correct Answer: High-energy electromagnetic photon
Question 93
What are isotopes?
Correct Answer: Nuclei having the same atomic number (Z) but different mass numbers (A)
Question 94
What are isobars?
Correct Answer: Nuclei having the same mass number (A) but different atomic numbers (Z)
Question 95
What are isotones?
Correct Answer: Nuclei having the same number of neutrons (N = A - Z)
Question 96
What is the curve of binding energy per nucleon versus mass number characterized by?
Correct Answer: A rapid rise up to A ≈ 30, a broad maximum around A = 50 to 80 (approx 8.5 MeV), and a slow decrease for heavier nuclei
Question 97
Why is nuclear fusion difficult to achieve in laboratory conditions on Earth?
Correct Answer: Because positively charged nuclei repel each other strongly and require extreme temperature and pressure to overcome Coulomb barrier
Question 98
What is a nuclear reactor controlled chain reaction based on?
Correct Answer: Controlled thermal neutron fission of Uranium-235
Question 99
What are moderators used for in a nuclear reactor?
Correct Answer: To slow down fast neutrons to thermal speeds
Question 100
What material is commonly used as control rods in a nuclear reactor to absorb excess neutrons?
Correct Answer: Cadmium or Boron
