1. How many fundamental forces exist in nature?
A) 2
B) 3
C) 4
D) 5
Answer: C) 4
Explanation: There are four fundamental forces – gravitational, electromagnetic, strong nuclear, and weak nuclear forces.
2. Which is the weakest fundamental force?
A) Strong nuclear force
B) Electromagnetic force
C) Gravitational force
D) Weak nuclear force
Answer: C) Gravitational force
Explanation: Gravity is the weakest but acts over infinite distances and governs celestial motions.
3. Which is the strongest fundamental force?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: A) Strong nuclear force
Explanation: Strong nuclear force binds protons and neutrons in nuclei; it is ~10³⁸ times stronger than gravity at short range.
4. Which force is responsible for the structure of the atom?
A) Weak nuclear force
B) Electromagnetic force
C) Gravitational force
D) Strong nuclear force
Answer: B) Electromagnetic force
Explanation: Electromagnetic force binds negatively charged electrons to the positively charged nucleus.
5. Which force causes beta decay in nuclei?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: B) Weak nuclear force
Explanation: The weak force allows neutrons to convert into protons, electrons, and neutrinos (beta decay).
6. Which force has infinite range?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Both B and C
Answer: C) Electromagnetic force
Explanation: Like gravity, electromagnetic force has infinite range but decreases with distance as 1/r².
7. The fundamental forces are mediated by:
A) Bosons
B) Fermions
C) Quarks
D) Neutrinos
Answer: A) Bosons
Explanation: Fundamental forces are carried by exchange particles (gauge bosons).
8. The strong nuclear force acts within:
A) 10⁻¹⁰ m
B) 10⁻⁶ m
C) 10⁻¹⁵ m
D) Infinite range
Answer: C) 10⁻¹⁵ m
Explanation: Strong force acts at subatomic distances (about 1 femtometer).
9. Which two forces act only at the subatomic level?
A) Gravity and Electromagnetic
B) Strong and Weak nuclear forces
C) Weak and Electromagnetic
D) Gravity and Strong nuclear
Answer: B) Strong and Weak nuclear forces
Explanation: Both are significant only at nuclear/particle scales.
10. Which force binds quarks inside protons and neutrons?
A) Electromagnetic force
B) Strong nuclear force
C) Weak nuclear force
D) Gravitational force
Answer: B) Strong nuclear force
Explanation: Gluons mediate the strong force, confining quarks within nucleons.
11. Which force has the shortest range?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: C) Weak nuclear force
Explanation: Weak force acts within ~10⁻¹⁸ m, much shorter than strong force.
12. The fundamental force that affects neutrinos is:
A) Electromagnetic force
B) Strong nuclear force
C) Weak nuclear force
D) Gravitational force
Answer: C) Weak nuclear force
Explanation: Neutrinos are neutral and only interact via weak force and gravity.
13. Which force is responsible for holding planets in orbit?
A) Weak nuclear force
B) Electromagnetic force
C) Gravitational force
D) Strong nuclear force
Answer: C) Gravitational force
Explanation: Gravitational force keeps planets bound to stars.
14. Which force is always attractive in nature?
A) Electromagnetic force
B) Strong nuclear force
C) Weak nuclear force
D) Gravitational force
Answer: D) Gravitational force
Explanation: Gravity always attracts, whereas others can be attractive or repulsive.
15. Which force can be both attractive and repulsive?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: B) Electromagnetic force
Explanation: Like charges repel; unlike charges attract.
16. Which force plays a role in nuclear fusion inside the Sun?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: B) Weak nuclear force
Explanation: Weak force allows proton-to-neutron conversion, enabling fusion.
17. Which fundamental force governs chemical bonding?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: C) Electromagnetic force
Explanation: Electromagnetic interactions between electrons and nuclei form chemical bonds.
18. The carrier particle of gravity is theoretically called:
A) Photon
B) Gluon
C) Graviton
D) W boson
Answer: C) Graviton
Explanation: Graviton is a hypothetical massless boson mediating gravity (not experimentally detected).
19. The photon mediates which force?
A) Gravity
B) Strong nuclear force
C) Electromagnetic force
D) Weak nuclear force
Answer: C) Electromagnetic force
Explanation: Photons are exchange particles of electromagnetic interaction.
20. Which particle mediates the strong nuclear force?
A) Photon
B) Gluon
C) W boson
D) Z boson
Answer: B) Gluon
Explanation: Gluons hold quarks together inside hadrons.
21. Which fundamental force violates parity (mirror symmetry)?
A) Gravitational force
B) Electromagnetic force
C) Weak nuclear force
D) Strong nuclear force
Answer: C) Weak nuclear force
Explanation: Weak interaction uniquely violates parity conservation.
22. The range of electromagnetic force is:
A) Infinite
B) 10⁻¹⁵ m
C) 10⁻¹⁸ m
D) Zero
Answer: A) Infinite
Explanation: Like gravity, it extends infinitely though weakens with distance.
23. The nuclear binding energy arises due to:
A) Gravitational force
B) Strong nuclear force
C) Weak nuclear force
D) Electromagnetic force
Answer: B) Strong nuclear force
Explanation: It is the energy from strong force binding nucleons.
24. Which force explains the large-scale structure of the universe?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: D) Gravitational force
Explanation: Gravity dominates at astronomical scales, shaping galaxies and cosmic structures.
25. Which force has coupling constant (strength factor) ≈ 1?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: A) Strong nuclear force
Explanation: The strong force has the highest coupling constant (~1), while others are much weaker.
26. The force of gravity between two bodies is given by:
A) F = k q₁q₂ / r²
B) F = G m₁m₂ / r²
C) F = mv² / r
D) F = G m / r
Answer: B) F = G m₁m₂ / r²
Explanation: Newton’s law of universal gravitation: the force between two masses is proportional to the product of masses and inversely proportional to the square of distance.
27. The value of the universal gravitational constant (G) is:
A) 6.67 × 10⁻¹¹ N·m²/kg²
B) 9.8 m/s²
C) 1.6 × 10⁻¹⁹ C
D) 3 × 10⁸ m/s
Answer: A) 6.67 × 10⁻¹¹ N·m²/kg²
Explanation: G is a fundamental constant appearing in Newton’s law of gravitation.
28. The acceleration due to gravity on Earth’s surface is approximately:
A) 9.8 m/s²
B) 6.67 × 10⁻¹¹ m/s²
C) 1 m/s²
D) 3 × 10⁸ m/s²
Answer: A) 9.8 m/s²
Explanation: The acceleration due to Earth’s gravity at sea level is ~9.8 m/s².
29. Coulomb’s law describes:
A) Magnetic force
B) Electrostatic force
C) Weak nuclear force
D) Gravitational force
Answer: B) Electrostatic force
Explanation: Coulomb’s law gives the electrostatic force between two charges: F = k q₁q₂ / r².
30. The unit of electric charge is:
A) Coulomb
B) Newton
C) Tesla
D) Joule
Answer: A) Coulomb
Explanation: The SI unit of electric charge is Coulomb (C).
31. The proportionality constant in Coulomb’s law is:
A) G
B) μ₀
C) k = 9 × 10⁹ N·m²/C²
D) h
Answer: C) k = 9 × 10⁹ N·m²/C²
Explanation: Electrostatic constant (k) appears in Coulomb’s law: F = k q₁q₂ / r².
32. Which is stronger at atomic scales, gravity or electrostatic force?
A) Gravity
B) Electrostatic force
C) Both equal
D) Cannot be compared
Answer: B) Electrostatic force
Explanation: Electrostatic force is ~10³⁶ times stronger than gravity at atomic level.
33. Which property makes gravity unique compared to other forces?
A) Acts only on charged particles
B) Always attractive
C) Has shortest range
D) Mediated by photons
Answer: B) Always attractive
Explanation: Gravity never repels, unlike electromagnetic force.
34. The Earth revolves around the Sun due to:
A) Weak force
B) Strong force
C) Gravitational force
D) Electromagnetic force
Answer: C) Gravitational force
Explanation: Sun’s gravity keeps Earth in its orbit.
35. The electric force between two charges doubles if distance is:
A) Halved
B) Doubled
C) Tripled
D) Reduced to one-fourth
Answer: A) Halved
Explanation: F ∝ 1/r²; halving distance increases force by 4 times.
36. The force responsible for lightning is:
A) Gravitational
B) Strong nuclear
C) Weak nuclear
D) Electromagnetic
Answer: D) Electromagnetic
Explanation: Lightning is caused by electrostatic discharge.
37. The ratio of electrostatic force to gravitational force between a proton and an electron is approximately:
A) 10²⁰
B) 10³⁶
C) 10⁻³⁶
D) 10⁶
Answer: B) 10³⁶
Explanation: Electrostatic force is vastly stronger than gravity at particle level.
38. The unit of gravitational force is:
A) Coulomb
B) Newton
C) Joule
D) Tesla
Answer: B) Newton
Explanation: Force (including gravitational) is measured in Newtons (N).
39. The weight of an object is:
A) Mass × velocity
B) Mass × acceleration due to gravity
C) Mass × height
D) Mass × charge
Answer: B) Mass × acceleration due to gravity
Explanation: W = m g, where g is acceleration due to gravity.
40. Which force is responsible for tides in oceans?
A) Electromagnetic force
B) Weak nuclear force
C) Gravitational force
D) Strong nuclear force
Answer: C) Gravitational force
Explanation: Tides are caused by the gravitational pull of the Moon and Sun.
41. The electric field is defined as:
A) Force per unit charge
B) Force per unit mass
C) Energy per unit charge
D) Potential per unit mass
Answer: A) Force per unit charge
Explanation: Electric field at a point = F/q.
42. The gravitational field is defined as:
A) Force per unit charge
B) Force per unit mass
C) Mass per unit force
D) Potential per unit charge
Answer: B) Force per unit mass
Explanation: Gravitational field strength = F/m.
43. Which of the following has both attractive and repulsive behavior?
A) Gravity
B) Weak nuclear force
C) Strong nuclear force
D) Electromagnetic force
Answer: D) Electromagnetic force
Explanation: Unlike charges attract, like charges repel.
44. Which constant appears in both Coulomb’s law and Gauss’s law?
A) h
B) ε₀ (permittivity of free space)
C) μ₀ (permeability of free space)
D) G
Answer: B) ε₀
Explanation: ε₀ relates to electric field in free space.
45. The gravitational potential energy of mass m at height h is:
A) mgh
B) ½ mv²
C) G m₁m₂ / r²
D) k q₁q₂ / r²
Answer: A) mgh
Explanation: Potential energy due to gravity = mgh.
46. The electric potential energy between two charges is:
A) mgh
B) ½ mv²
C) k q₁q₂ / r
D) G m₁m₂ / r²
Answer: C) k q₁q₂ / r
Explanation: U = k q₁q₂ / r is potential energy in electrostatics.
47. Which fundamental force governs satellite motion?
A) Electromagnetic
B) Weak nuclear
C) Gravitational
D) Strong nuclear
Answer: C) Gravitational
Explanation: Gravity keeps satellites in orbit around Earth.
48. Which particle mediates the electromagnetic force?
A) Photon
B) Gluon
C) Graviton
D) W boson
Answer: A) Photon
Explanation: Photons are force carriers of electromagnetic interaction.
49. Which constant defines the strength of gravitational interaction?
A) ε₀
B) μ₀
C) G
D) h
Answer: C) G
Explanation: G is the universal gravitational constant.
50. Which constant defines the strength of electrostatic interaction?
A) G
B) ε₀
C) μ₀
D) k (1/4πε₀)
Answer: D) k (1/4πε₀)
Explanation: Electrostatic constant k = 1/4πε₀ governs electric force.
51. Which is the strongest fundamental force in nature?
A) Gravitational force
B) Electromagnetic force
C) Strong nuclear force
D) Weak nuclear force
Answer: C) Strong nuclear force
Explanation: The strong nuclear force binds nucleons (protons and neutrons) in the nucleus and is the strongest force, but it acts only over very short distances (~10⁻¹⁵ m).
52. Which particle mediates the strong nuclear force?
A) Photon
B) Gluon
C) W boson
D) Z boson
Answer: B) Gluon
Explanation: Gluons are massless exchange particles that bind quarks inside protons and neutrons.
53. The weak nuclear force is mediated by:
A) Photon
B) Gluon
C) W and Z bosons
D) Graviton
Answer: C) W and Z bosons
Explanation: W⁺, W⁻, and Z⁰ bosons are heavy particles that carry the weak force, explaining its short range.
54. Which force is responsible for radioactive beta decay?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: C) Weak nuclear force
Explanation: Beta decay occurs when a neutron converts into a proton, electron, and antineutrino via weak interaction.
55. The strong force becomes negligible beyond:
A) 10⁻¹⁵ m
B) 10⁻¹⁸ m
C) 10⁻¹⁰ m
D) 1 m
Answer: A) 10⁻¹⁵ m
Explanation: Strong nuclear force is effective only up to femtometer distances inside the nucleus.
56. Which force prevents the nucleus from flying apart due to proton-proton repulsion?
A) Weak nuclear force
B) Strong nuclear force
C) Gravitational force
D) Electromagnetic force
Answer: B) Strong nuclear force
Explanation: Strong force overcomes the repulsive electrostatic force between protons inside the nucleus.
57. Quarks are confined inside nucleons due to:
A) Gravity
B) Electromagnetic force
C) Strong force
D) Weak force
Answer: C) Strong force
Explanation: Gluons bind quarks together, ensuring they cannot exist freely (quark confinement).
58. Which force explains the Sun’s energy production?
A) Gravitational force
B) Weak nuclear force
C) Strong nuclear force
D) Electromagnetic force
Answer: B) Weak nuclear force
Explanation: Weak force converts protons into neutrons in hydrogen fusion inside the Sun.
59. Which force is responsible for nuclear fission and fusion?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: A) Strong nuclear force
Explanation: Binding energy from the strong force governs both fission (splitting) and fusion (combining).
60. Which interaction violates parity conservation?
A) Strong force
B) Weak force
C) Electromagnetic force
D) Gravitational force
Answer: B) Weak force
Explanation: Weak nuclear force is unique in violating parity (mirror symmetry) and charge-parity (CP) conservation.
61. Which force has the shortest range?
A) Weak nuclear force
B) Strong nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: A) Weak nuclear force
Explanation: Its range is ~10⁻¹⁸ m, much shorter than the strong nuclear force (~10⁻¹⁵ m).
62. Which bosons are massive among the fundamental force carriers?
A) Photon and Gluon
B) W and Z bosons
C) Graviton
D) All are massless
Answer: B) W and Z bosons
Explanation: W and Z bosons are heavy, giving weak interaction its short range.
63. The residual strong force between nucleons is called:
A) Yukawa force
B) Coulomb force
C) Lorentz force
D) Newtonian force
Answer: A) Yukawa force
Explanation: Hideki Yukawa proposed that pions mediate the residual nuclear force between nucleons.
64. Which particle is exchanged in the Yukawa model of nuclear force?
A) Proton
B) Pion (π-meson)
C) Neutrino
D) Photon
Answer: B) Pion (π-meson)
Explanation: Yukawa suggested that pions carry the residual strong interaction between nucleons.
65. The weak nuclear force is essential for the existence of:
A) Neutron stars
B) Neutrino interactions
C) Black holes
D) Electromagnetic waves
Answer: B) Neutrino interactions
Explanation: Neutrinos interact only via weak force and gravity, not by strong or electromagnetic forces.
66. Which force is responsible for the proton-proton chain in stars?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: B) Weak nuclear force
Explanation: Weak force enables proton conversion, starting nuclear fusion in stars.
67. Which property is unique to strong nuclear force at very short distances (<0.7 fm)?
A) Always attractive
B) Becomes repulsive
C) Infinite range
D) Mediated by photons
Answer: B) Becomes repulsive
Explanation: At extremely short distances, the strong force turns repulsive, preventing nucleons from collapsing.
68. Which interaction explains the decay of a neutron into a proton?
A) Strong nuclear force
B) Weak nuclear force
C) Gravitational force
D) Electromagnetic force
Answer: B) Weak nuclear force
Explanation: Neutron decay (beta decay) occurs via the weak force.
69. Which force ensures the stability of atomic nuclei?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: A) Strong nuclear force
Explanation: It binds protons and neutrons tightly against Coulomb repulsion.
70. Which process involves the weak force?
A) Alpha decay
B) Beta decay
C) Gamma emission
D) Coulomb attraction
Answer: B) Beta decay
Explanation: Only beta decay involves weak interaction; alpha and gamma are governed by other forces.
71. The weak force was unified with electromagnetic force into:
A) Quantum Chromodynamics (QCD)
B) Electroweak theory
C) General Relativity
D) Newtonian mechanics
Answer: B) Electroweak theory
Explanation: The electroweak theory (Glashow–Salam–Weinberg model) unifies electromagnetic and weak forces.
72. Which particle decays due to the weak interaction?
A) Proton (in free state)
B) Neutron (in free state)
C) Photon
D) Gluon
Answer: B) Neutron (in free state)
Explanation: Free neutrons decay into a proton, electron, and antineutrino through weak force.
73. The strong interaction is described mathematically by:
A) Electroweak theory
B) General Relativity
C) Quantum Chromodynamics (QCD)
D) Quantum Electrodynamics (QED)
Answer: C) Quantum Chromodynamics (QCD)
Explanation: QCD explains how gluons mediate the strong interaction.
74. Which property of quarks is linked to the strong force?
A) Mass
B) Spin
C) Color charge
D) Electric charge
Answer: C) Color charge
Explanation: Quarks carry “color charge,” and gluons mediate strong interaction between them.
75. Which interaction is primarily responsible for supernova explosions?
A) Electromagnetic force
B) Strong nuclear force
C) Weak nuclear force
D) Gravitational force
Answer: C) Weak nuclear force
Explanation: Weak interactions involving neutrinos play a crucial role in core-collapse supernovae.
76. Which force is primarily responsible for holding a star like the Sun together against thermal pressure?
A) Electromagnetic force
B) Strong nuclear force
C) Weak nuclear force
D) Gravitational force
Answer: D) Gravitational force
Explanation: Gravity pulls the star’s mass inward; it balances the outward pressure from fusion so the star remains in hydrostatic equilibrium.
77. Which force allows neutrinos produced in the Sun’s core to escape almost unimpeded?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: C) Weak nuclear force
Explanation: Neutrinos interact only via the weak force (and gravity), so they have very small interaction cross-sections and pass through matter easily.
78. In nuclear fusion (proton–proton chain), which interaction is directly responsible for converting a proton into a neutron?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravitational force
Answer: B) Weak nuclear force
Explanation: The weak interaction enables a proton to change flavor (to a neutron) by emitting a positron and a neutrino — a necessary step in the p–p chain.
79. Which force must be overcome for two positively charged nuclei to get close enough to fuse?
A) Gravitational force
B) Weak force
C) Electromagnetic force (Coulomb barrier)
D) Strong force
Answer: C) Electromagnetic force (Coulomb barrier)
Explanation: Like charges repel via Coulomb force; quantum tunneling and high temperatures help nuclei overcome this barrier so the strong force can bind them.
80. In particle accelerators, quarks are never observed in isolation because of:
A) Electromagnetic shielding
B) Color confinement from the strong force
C) Weak-force decay
D) Gravitational attraction
Answer: B) Color confinement from the strong force
Explanation: QCD predicts quarks are confined — attempting to separate them produces new quark–antiquark pairs, so only color-neutral hadrons appear.
81. The energy released per nucleon when iron-56 fuses or splits is minimal compared to other nuclei. This is because:
A) Iron has the weakest strong force
B) Iron has the highest binding energy per nucleon
C) Iron is electrically neutral
D) Iron is unstable
Answer: B) Iron has the highest binding energy per nucleon
Explanation: Nuclei lighter than iron release energy by fusion; heavier ones release energy by fission. Iron-56 sits near the binding-energy peak.
82. Which fundamental interaction is modeled by Quantum Electrodynamics (QED)?
A) Strong nuclear force
B) Weak nuclear force
C) Electromagnetic force
D) Gravity
Answer: C) Electromagnetic force
Explanation: QED is the quantum field theory describing how charged particles interact by exchanging photons.
83. A muon decays into an electron and two neutrinos. Which fundamental force causes this decay?
A) Strong force
B) Electromagnetic force
C) Weak force
D) Gravitational force
Answer: C) Weak force
Explanation: Lepton decays (like muon → electron + neutrinos) proceed via the weak interaction mediated by W bosons.
84. Which force dominates the behavior of electrons in chemical reactions?
A) Strong nuclear force
B) Electromagnetic force
C) Weak nuclear force
D) Gravitational force
Answer: B) Electromagnetic force
Explanation: Chemical bonds and electron behavior are governed by electromagnetic interactions between electrons and nuclei.
85. Why are gravitational effects negligible in atoms compared to electromagnetic effects?
A) Gravity acts only on large scales
B) Gravitational constant G is extremely small so gravitational forces between subatomic particles are tiny compared to electrostatic forces
C) Atoms are electrically neutral
D) Gravity is repulsive at small scales
Answer: B) Gravitational constant G is extremely small so gravitational forces between subatomic particles are tiny compared to electrostatic forces
Explanation: The ratio of electrostatic to gravitational force between electron and proton ≈ 10³⁹ — electrostatic wins decisively at atomic scales.
86. The strong nuclear force gets weaker at very high energies / short distances — this property is called:
A) Confinement
B) Asymptotic freedom
C) Parity violation
D) Screening
Answer: B) Asymptotic freedom
Explanation: In QCD, quarks interact more weakly at extremely short distances (high momentum transfer), allowing perturbative calculations.
87. Which force is chiefly responsible for the pressure that resists gravitational collapse in a white dwarf?
A) Degeneracy pressure from electrons (a quantum effect arising ultimately from electromagnetic interactions)
B) Thermal pressure from fusion (strong force)
C) Weak interaction pressure
D) Gravitational pressure
Answer: A) Degeneracy pressure from electrons (a quantum effect arising ultimately from electromagnetic interactions)
Explanation: Electron degeneracy pressure (Pauli exclusion principle) halts collapse; electromagnetism determines atomic structure that underlies this pressure.
88. During a core-collapse supernova, which particle interactions (and associated force) play a major role in reviving the shockwave that ejects the outer layers?
A) Photons via electromagnetic force
B) Neutrinos via weak interactions
C) Gluons via strong force
D) Gravitons via gravity
Answer: B) Neutrinos via weak interactions
Explanation: Enormous neutrino fluxes deposit energy in the stalled shock through weak interactions, aiding the explosion mechanism.
89. Which force’s quantum (gauge boson) has not been experimentally detected?
A) Photon (EM)
B) Gluon (strong)
C) W and Z (weak)
D) Graviton (gravity)
Answer: D) Graviton (gravity)
Explanation: Photons, gluons, W/Z bosons are observed or inferred; a quantum theory of gravity and direct detection of gravitons remain unestablished.
90. In Rutherford scattering, the deflection of alpha particles by a nucleus is primarily due to:
A) Strong nuclear force at all distances
B) Electromagnetic (Coulomb) interaction between alpha particle and nucleus
C) Weak nuclear force
D) Gravitational attraction
Answer: B) Electromagnetic (Coulomb) interaction between alpha particle and nucleus
Explanation: At the distances relevant to Rutherford scattering, Coulomb repulsion dominates; only very close approach involves nuclear forces.
91. The electric potential at a point due to a point charge q at distance r is V = kq/r. The analogous gravitational potential due to mass M is:
A) V = G M / r (but negative sign conventionally used)
B) V = k M / r
C) V = G M r
D) V = GM/r²
Answer: A) V = G M / r (but negative sign conventionally used)
Explanation: Gravitational potential (per unit mass) is −GM/r; magnitude follows inverse r law analogous to electrostatics.
92. Magnetic forces between current-carrying wires arise from:
A) Strong nuclear force
B) Electrostatic attraction only
C) The electromagnetic interaction (motion of charges and its magnetic component)
D) Weak force exchange
Answer: C) The electromagnetic interaction (motion of charges and its magnetic component)
Explanation: Moving charges produce magnetic fields; magnetic forces are part of the electromagnetic interaction described by Maxwell’s equations and special relativity.
93. Which statement about the range of the four forces is correct?
A) Gravity and electromagnetism have infinite range; strong and weak forces are short-range.
B) All four have infinite range.
C) Strong force has infinite range; others are short-range.
D) Weak force has infinite range; others are short-range.
Answer: A) Gravity and electromagnetism have infinite range; strong and weak forces are short-range.
Explanation: Massless carriers (photon, graviton hypothetically) give infinite range; massive carriers (W, Z) give short range; strong force is short-range due to confinement.
94. Charge conjugation, parity, and time reversal symmetries (C, P, T) are important in particle physics. Which interaction is known to violate CP symmetry (combined charge-parity)?
A) Electromagnetic force
B) Strong force (so far CP-conserving in observation)
C) Weak force
D) Gravity
Answer: C) Weak force
Explanation: Weak interactions exhibit CP violation (observed in kaon and B-meson systems), a key ingredient for matter–antimatter asymmetry.
95. The concept of effective field theories allows physicists to treat low-energy phenomena without full details of high-energy physics. Which force often requires such effective descriptions at nuclear scales (e.g., nucleon interactions)?
A) Gravity only
B) Electromagnetism only
C) Strong interaction (residual nuclear forces modeled by pion exchange, etc.)
D) Weak interaction only
Answer: C) Strong interaction (residual nuclear forces modeled by pion exchange, etc.)
Explanation: QCD is fundamental, but low-energy nuclear forces are often modeled by effective theories (Yukawa pion exchange, chiral EFT).
96. If you double the distance between two point masses, the gravitational force becomes:
A) Twice as large
B) Half as large
C) One quarter as large
D) Four times as large
Answer: C) One quarter as large
Explanation: Newton’s law: F ∝ 1/r². Doubling r reduces force by (1/2)² = 1/4.
97. Two point charges +q and −q are separated by distance d. The net electric field at the midpoint is:
A) Zero
B) Non-zero directed toward the positive charge
C) Non-zero directed toward the negative charge
D) Infinite
Answer: A) Zero
Explanation: Equal and opposite charges produce equal-magnitude fields at the midpoint pointing in opposite directions; they cancel.
98. In beta-plus decay (a proton converting into a neutron plus a positron and neutrino), which force is responsible?
A) Electromagnetic
B) Strong nuclear
C) Weak nuclear
D) Gravitational
Answer: C) Weak nuclear
Explanation: Beta-plus decay proceeds via the weak interaction mediated by W⁺ boson emission.
99. Which force would be most important to consider when calculating the trajectory of a comet passing near Jupiter?
A) Strong nuclear force
B) Electromagnetic force
C) Gravitational force
D) Weak nuclear force
Answer: C) Gravitational force
Explanation: Large-scale celestial motions are dominated by gravity; other forces are negligible for neutral macroscopic bodies.
100. A proton and alpha particle (He²⁺) are brought very close. Which forces will determine whether they stick (nuclear capture) or repel?
A) Only gravity
B) Electromagnetic repulsion at larger separations, and strong nuclear attraction at very short separations
C) Only electromagnetic attraction
D) Only weak force
Answer: B) Electromagnetic repulsion at larger separations, and strong nuclear attraction at very short separations
Explanation: Coulomb repulsion (both positive) prevents approach; if kinetic energy (or tunneling) brings them into femtometer distances, the strong force can bind them—provided the system is energetically favorable.