These 50 important Modern Physics MCQs cover photoelectric effect, dual nature of matter, de Broglie wavelength, Bohr’s model, atomic spectra, nuclear physics, radioactivity, mass defect, binding energy, fission, fusion and semiconductors.
1. The energy of a photon is given by:
A. h/ν
B. hν
C. ν/h
D. hcν
Answer: B. hν
2. The momentum of a photon having wavelength λ is:
A. hλ
B. h/λ
C. λ/h
D. hc/λ
Answer: B. h/λ
3. In the photoelectric effect, the maximum kinetic energy of emitted electrons depends on:
A. Intensity of incident light only
B. Frequency of incident light
C. Area of metal surface
D. Number of electrons in the metal
Answer: B. Frequency of incident light
4. The minimum frequency required to eject electrons from a metal surface is called:
A. Resonance frequency
B. Threshold frequency
C. Critical frequency
D. Natural frequency
Answer: B. Threshold frequency
5. Einstein's photoelectric equation is:
A. hν = φ − Kmax
B. hν = φ + Kmax
C. hν = Kmax − φ
D. φ = hν + Kmax
Answer: B. hν = φ + Kmax
6. If the frequency of incident radiation is increased above the threshold frequency, the stopping potential:
A. Decreases
B. Remains constant
C. Increases
D. Becomes zero
Answer: C. Increases
7. Increasing the intensity of incident light while keeping its frequency constant generally increases:
A. Maximum kinetic energy
B. Stopping potential
C. Photoelectric current
D. Work function
Answer: C. Photoelectric current
8. The work function of a metal is 2 eV. Light of photon energy 5 eV falls on it. The maximum kinetic energy of emitted electrons is:
A. 2 eV
B. 3 eV
C. 5 eV
D. 7 eV
Answer: B. 3 eV
9. The de Broglie wavelength of a particle having momentum p is:
A. hp
B. h/p
C. p/h
D. hc/p
Answer: B. h/p
10. If the velocity of a particle is doubled, its de Broglie wavelength becomes:
A. Double
B. Half
C. Four times
D. Unchanged
Answer: B. Half
11. The de Broglie wavelength of an electron accelerated through potential V is proportional to:
A. √V
B. V
C. 1/√V
D. 1/V
Answer: C. 1/√V
12. Which experiment experimentally verified the wave nature of electrons?
A. Rutherford experiment
B. Davisson-Germer experiment
C. Millikan experiment
D. Franck-Hertz experiment
Answer: B. Davisson-Germer experiment
13. According to Bohr's quantization condition:
A. mvr = nh
B. mvr = nh/2π
C. mvr = 2πnh
D. mvr = h/n
Answer: B. mvr = nh/2π
14. The radius of the nth Bohr orbit of hydrogen is proportional to:
A. n
B. n²
C. 1/n
D. 1/n²
Answer: B. n²
15. The energy of an electron in the nth orbit of hydrogen atom is:
A. −13.6/n eV
B. −13.6/n² eV
C. 13.6n² eV
D. −13.6n eV
Answer: B. −13.6/n² eV
16. The ground-state energy of a hydrogen atom is:
A. 13.6 eV
B. −13.6 eV
C. −3.4 eV
D. 0 eV
Answer: B. −13.6 eV
17. The ionization energy of hydrogen atom in the ground state is:
A. 3.4 eV
B. 10.2 eV
C. 13.6 eV
D. 27.2 eV
Answer: C. 13.6 eV
18. When an electron jumps from n = 3 to n = 2 in hydrogen atom, radiation belonging to which series is emitted?
A. Lyman
B. Balmer
C. Paschen
D. Brackett
Answer: B. Balmer
19. The Lyman series lies mainly in the:
A. Visible region
B. Infrared region
C. Ultraviolet region
D. Microwave region
Answer: C. Ultraviolet region
20. The Balmer series lies mainly in the:
A. Ultraviolet region
B. Visible region
C. Infrared region
D. X-ray region
Answer: B. Visible region
21. The Paschen series corresponds to transitions ending at:
A. n = 1
B. n = 2
C. n = 3
D. n = 4
Answer: C. n = 3
22. Rutherford's α-particle scattering experiment established that:
A. Electrons are stationary
B. Atoms are completely solid
C. Positive charge is concentrated in a small nucleus
D. Neutrons revolve around the nucleus
Answer: C. Positive charge is concentrated in a small nucleus
23. According to Rutherford's model, most of the atom is:
A. Filled with positive charge
B. Empty space
C. Filled with neutrons
D. Filled with electrons
Answer: B. Empty space
24. The atomic number of an element represents the number of:
A. Neutrons
B. Protons
C. Nucleons
D. Protons + neutrons
Answer: B. Protons
25. The mass number of a nucleus is equal to:
A. Number of protons only
B. Number of neutrons only
C. Number of protons + neutrons
D. Number of electrons + protons
Answer: C. Number of protons + neutrons
26. Isotopes have:
A. Same mass number and different atomic numbers
B. Same atomic number and different mass numbers
C. Different atomic numbers and same neutron number
D. Same number of neutrons only
Answer: B. Same atomic number and different mass numbers
27. The relation between radioactive decay constant λ and half-life T₁/₂ is:
A. T₁/₂ = λ/0.693
B. T₁/₂ = 0.693λ
C. T₁/₂ = 0.693/λ
D. T₁/₂ = 1/λ²
Answer: C. T₁/₂ = 0.693/λ
28. If the half-life of a radioactive substance is 10 days, what fraction remains after 30 days?
A. 1/2
B. 1/4
C. 1/8
D. 1/16
Answer: C. 1/8
29. The SI unit of radioactivity is:
A. Curie
B. Becquerel
C. Roentgen
D. Gray
Answer: B. Becquerel
30. In alpha decay, the mass number of the nucleus decreases by:
A. 1
B. 2
C. 4
D. 8
Answer: C. 4
31. In alpha decay, the atomic number decreases by:
A. 1
B. 2
C. 3
D. 4
Answer: B. 2
32. In β⁻ decay, a neutron changes into:
A. Proton + electron + antineutrino
B. Proton + positron
C. Electron + neutron
D. Proton + alpha particle
Answer: A. Proton + electron + antineutrino
33. Gamma rays are:
A. Charged particles
B. Helium nuclei
C. Electromagnetic radiation
D. Electrons
Answer: C. Electromagnetic radiation
34. Which radiation has the highest penetrating power among α, β and γ rays?
A. Alpha
B. Beta
C. Gamma
D. All have equal penetration
Answer: C. Gamma
35. Nuclear binding energy is related to:
A. Atomic radius
B. Mass defect
C. Atomic number only
D. Number of electrons
Answer: B. Mass defect
36. Einstein's mass-energy relation is:
A. E = mc
B. E = mc²
C. E = m/c²
D. E = c/m
Answer: B. E = mc²
37. A nucleus with greater binding energy per nucleon is generally:
A. Less stable
B. More stable
C. Always radioactive
D. Always unstable
Answer: B. More stable
38. Nuclear fission involves:
A. Combining two light nuclei
B. Splitting a heavy nucleus into lighter nuclei
C. Emission of electrons only
D. Formation of atoms from electrons
Answer: B. Splitting a heavy nucleus into lighter nuclei
39. Nuclear fusion involves:
A. Splitting a heavy nucleus
B. Combining light nuclei to form a heavier nucleus
C. Removing electrons from atoms
D. Emission of gamma rays only
Answer: B. Combining light nuclei to form a heavier nucleus
40. The energy of the Sun is primarily produced by:
A. Nuclear fission
B. Nuclear fusion
C. Chemical combustion
D. Radioactive decay
Answer: B. Nuclear fusion
41. A semiconductor has electrical conductivity:
A. Greater than a conductor
B. Between that of conductors and insulators
C. Zero at all temperatures
D. Always equal to an insulator
Answer: B. Between that of conductors and insulators
42. A pure semiconductor is called:
A. Extrinsic semiconductor
B. Intrinsic semiconductor
C. Metallic semiconductor
D. Ionic semiconductor
Answer: B. Intrinsic semiconductor
43. Silicon and germanium are examples of:
A. Conductors
B. Semiconductors
C. Insulators
D. Superconductors
Answer: B. Semiconductors
44. In an n-type semiconductor, the majority charge carriers are:
A. Holes
B. Electrons
C. Protons
D. Neutrons
Answer: B. Electrons
45. In a p-type semiconductor, the majority charge carriers are:
A. Electrons
B. Holes
C. Neutrons
D. Ions
Answer: B. Holes
46. An n-type semiconductor is obtained by doping pure silicon with:
A. Trivalent impurity
B. Pentavalent impurity
C. Divalent impurity
D. Monovalent impurity
Answer: B. Pentavalent impurity
47. A p-type semiconductor is obtained by doping silicon with:
A. Pentavalent impurity
B. Hexavalent impurity
C. Trivalent impurity
D. Monovalent impurity
Answer: C. Trivalent impurity
48. A p-n junction diode allows current to flow mainly:
A. Equally in both directions
B. Only in reverse direction
C. In forward direction with much lower resistance
D. Only when cooled to 0 K
Answer: C. In forward direction with much lower resistance
49. In an LED, electrical energy is primarily converted into:
A. Sound energy
B. Light energy
C. Nuclear energy
D. Mechanical energy
Answer: B. Light energy
50. Which phenomenon demonstrates the particle nature of electromagnetic radiation?
A. Interference
B. Diffraction
C. Photoelectric effect
D. Polarisation
Answer: C. Photoelectric effect
Important Topics Covered
Photon and photon energy
Photoelectric effect
Einstein's photoelectric equation
Work function and threshold frequency
de Broglie hypothesis
Davisson-Germer experiment
Bohr atomic model
Hydrogen spectrum
Rutherford model
Atomic number and mass number
Isotopes
Radioactive decay
Alpha, beta and gamma radiation
Half-life and decay constant
Mass defect and binding energy
Nuclear fission and fusion
Semiconductor basics
Intrinsic and extrinsic semiconductors
n-type and p-type semiconductors
p-n junction diode
LED
