Q.1 Who proposed the quantum theory of radiation?
Albert Einstein
Max Planck
Niels Bohr
Louis de Broglie
Explanation - Max Planck proposed the quantum theory in 1900 by introducing the concept of energy quanta to explain blackbody radiation.
Correct answer is: Max Planck
Q.2 What is the energy of a photon with frequency ν?
hν
hc/ν
ν/h
h/ν
Explanation - The energy of a photon is directly proportional to its frequency: E = hν, where h is Planck’s constant.
Correct answer is: hν
Q.3 The photoelectric effect proves which nature of light?
Wave nature
Particle nature
Both wave and particle
Magnetic nature
Explanation - The photoelectric effect shows that light interacts with matter in discrete quanta (photons), proving its particle nature.
Correct answer is: Particle nature
Q.4 In the photoelectric effect, the stopping potential depends on:
Frequency of incident light
Intensity of incident light
Surface area of the metal
Temperature of the metal
Explanation - Stopping potential depends on the maximum kinetic energy of emitted electrons, which is related to the frequency of light.
Correct answer is: Frequency of incident light
Q.5 The threshold frequency in photoelectric effect is:
Frequency below which emission occurs
Frequency above which emission stops
Minimum frequency required to eject electrons
Frequency at which intensity is maximum
Explanation - Threshold frequency is the minimum frequency of light needed to overcome the work function of the metal and emit electrons.
Correct answer is: Minimum frequency required to eject electrons
Q.6 Who explained the photoelectric effect successfully?
Max Planck
Albert Einstein
Niels Bohr
James Clerk Maxwell
Explanation - Einstein explained the photoelectric effect using photons, earning him the Nobel Prize in 1921.
Correct answer is: Albert Einstein
Q.7 The de Broglie wavelength of a particle is given by:
h/p
p/h
hv/c
hν
Explanation - Louis de Broglie proposed that matter exhibits wave nature, with wavelength λ = h/p, where p is momentum.
Correct answer is: h/p
Q.8 For an electron accelerated through potential difference V, de Broglie wavelength is proportional to:
1/√V
√V
V
1/V
Explanation - λ = h / √(2meV). Thus, wavelength decreases as the square root of the accelerating potential.
Correct answer is: 1/√V
Q.9 The Davisson-Germer experiment proved:
Wave nature of light
Wave nature of electrons
Particle nature of protons
Quantum theory of photons
Explanation - The Davisson-Germer experiment showed electron diffraction, proving wave nature of matter.
Correct answer is: Wave nature of electrons
Q.10 In Bohr’s hydrogen atom, the angular momentum of electron is:
nh
nh/2π
n²h/2π
nħ
Explanation - Bohr postulated that the angular momentum of the electron is quantized: L = nh/2π.
Correct answer is: nh/2π
Q.11 Energy of the nth orbit in Bohr’s hydrogen atom is proportional to:
1/n
n
1/n²
n²
Explanation - Energy levels in hydrogen are quantized as En = -13.6 eV/n², proportional to 1/n².
Correct answer is: 1/n²
Q.12 The ionization energy of hydrogen atom is:
10.2 eV
13.6 eV
3.4 eV
0 eV
Explanation - Ionization energy is the energy required to remove the electron from n=1 orbit to infinity, which is 13.6 eV.
Correct answer is: 13.6 eV
Q.13 The spectral series of hydrogen atom in UV region is:
Balmer series
Lyman series
Paschen series
Brackett series
Explanation - Lyman series corresponds to transitions ending at n=1, lying in the UV region.
Correct answer is: Lyman series
Q.14 Which series of hydrogen spectrum lies in the visible region?
Lyman
Balmer
Paschen
Pfund
Explanation - The Balmer series corresponds to transitions ending at n=2 and appears in the visible region.
Correct answer is: Balmer
Q.15 X-rays are produced when:
Electrons strike the target
Protons strike the target
Photons collide
Neutrons are captured
Explanation - X-rays are generated when high-speed electrons hit a metal target and decelerate rapidly.
Correct answer is: Electrons strike the target
Q.16 Which scientist discovered X-rays?
Wilhelm Roentgen
Henri Becquerel
Marie Curie
Chadwick
Explanation - X-rays were discovered by Wilhelm Roentgen in 1895 while working with cathode rays.
Correct answer is: Wilhelm Roentgen
Q.17 In X-ray tubes, continuous spectrum is due to:
Transition of electrons
Deceleration of electrons
Nuclear reaction
Gamma radiation
Explanation - Continuous X-ray spectrum arises from Bremsstrahlung radiation due to sudden deceleration of electrons.
Correct answer is: Deceleration of electrons
Q.18 Characteristic X-rays are produced due to:
Electron transition within atom
Gamma decay
Nuclear fission
Free electrons
Explanation - Characteristic X-rays result from transitions of inner-shell electrons in atoms after ejection.
Correct answer is: Electron transition within atom
Q.19 The wavelength of X-rays is of the order of:
10⁻² m
10⁻⁵ m
10⁻¹⁰ m
10⁻¹⁵ m
Explanation - X-rays typically have wavelengths around 0.01–10 nm, i.e., of the order 10⁻¹⁰ m.
Correct answer is: 10⁻¹⁰ m
Q.20 Radioactivity was discovered by:
Wilhelm Roentgen
Henri Becquerel
Rutherford
Bohr
Explanation - Henri Becquerel discovered natural radioactivity in 1896 while studying uranium salts.
Correct answer is: Henri Becquerel
Q.21 Which radiation has the highest penetrating power?
Alpha rays
Beta rays
Gamma rays
X-rays
Explanation - Gamma rays are highly energetic electromagnetic waves and penetrate deeply compared to alpha and beta particles.
Correct answer is: Gamma rays
Q.22 Half-life of a radioactive substance is the time in which:
All nuclei decay
Half the nuclei decay
Nucleus becomes stable
Radiation stops
Explanation - Half-life is the time required for half of the radioactive nuclei in a sample to decay.
Correct answer is: Half the nuclei decay
Q.23 Unit of radioactivity is:
Joule
Becquerel
Tesla
Newton
Explanation - Radioactivity is measured in Becquerel (Bq), defined as one disintegration per second.
Correct answer is: Becquerel
Q.24 Which isotope is used in carbon dating?
C-12
C-13
C-14
C-16
Explanation - Carbon dating uses the radioactive isotope Carbon-14 to estimate the age of organic remains.
Correct answer is: C-14
Q.25 Mass defect in a nucleus is due to:
Electrons lost
Protons expelled
Binding energy
Fission reaction
Explanation - Mass defect is the difference between the mass of nucleons and actual nucleus mass, due to nuclear binding energy.
Correct answer is: Binding energy