PHYSICS PRELIMINARY EXAM (PRELIMS)
QUESTION AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES
2026 Q&A INSTANT DOWNLOAD PDF
1. A particle moves under a central force 𝐹(𝑟) = −𝑘/𝑟 2 . The orbit is
A. Elliptical, parabolic, or hyperbolic
B. Circular only
C. Linear
D. Spiral
Answer: A
Rationale: Inverse-square central forces lead to conic-section orbits
depending on total energy.
2. The Poisson bracket {𝑞𝑖 , 𝑝𝑗 }equals
A. 0
B. 𝛿𝑖𝑗
C. 𝑖ℏ
D. −𝛿𝑖𝑗
Answer: B
Rationale: Canonical coordinates satisfy {𝑞𝑖 , 𝑝𝑗 } = 𝛿𝑖𝑗 .
3. The Lagrangian for a free relativistic particle is proportional to
A. 𝑣 2
B. √1 − 𝑣 2 /𝑐 2
C. −𝑚𝑐 2 √1 − 𝑣 2 /𝑐 2
D. 𝑚𝑐 2 (1 − 𝑣 2 /𝑐 2 )
, Answer: C
Rationale: The relativistic action uses proper time, giving this Lagrangian.
4. The dimension of action is
A. Energy
B. Energy × time
C. Momentum
D. Force × time
Answer: B
Rationale: Action has units of joule-seconds, same as angular momentum.
5. A conserved quantity associated with time translation invariance is
A. Momentum
B. Angular momentum
C. Energy
D. Charge
Answer: C
Rationale: Noether’s theorem links time invariance to energy
conservation.
Electrodynamics
6. Gauss’s law in differential form is
A. ∇ ⋅ 𝐄 = 0
B. ∇ × 𝐄 = − ∂𝐁/ ∂𝑡
C. ∇ ⋅ 𝐄 = 𝜌/𝜀0
D. ∇ × 𝐁 = 0
Answer: C
Rationale: Electric field divergence equals charge density over
permittivity.
7. The vector potential gauge freedom implies
A. Physical fields change
B. Only scalar potential matters
, C. Potentials are not unique
D. Magnetic field vanishes
Answer: C
Rationale: Different potentials can give the same electric and magnetic
fields.
8. The Poynting vector represents
A. Energy density
B. Momentum density
C. Energy flux
D. Charge flow
Answer: C
Rationale: 𝐒 = 𝐄 × 𝐇gives energy flow per unit area.
9. Electromagnetic waves in vacuum travel at
A. 1/√𝜇0 𝜀0
B. √𝜇0 𝜀0
C. 𝑐 2
D. 𝜇0 𝜀0
Answer: A
Rationale: Maxwell’s equations predict wave speed 𝑐 = 1/√𝜇0 𝜀0 .
10.The displacement current term ensures conservation of
A. Energy
B. Charge
C. Momentum
D. Mass
Answer: B
Rationale: It guarantees continuity equation consistency.
Quantum Mechanics
QUESTION AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES
2026 Q&A INSTANT DOWNLOAD PDF
1. A particle moves under a central force 𝐹(𝑟) = −𝑘/𝑟 2 . The orbit is
A. Elliptical, parabolic, or hyperbolic
B. Circular only
C. Linear
D. Spiral
Answer: A
Rationale: Inverse-square central forces lead to conic-section orbits
depending on total energy.
2. The Poisson bracket {𝑞𝑖 , 𝑝𝑗 }equals
A. 0
B. 𝛿𝑖𝑗
C. 𝑖ℏ
D. −𝛿𝑖𝑗
Answer: B
Rationale: Canonical coordinates satisfy {𝑞𝑖 , 𝑝𝑗 } = 𝛿𝑖𝑗 .
3. The Lagrangian for a free relativistic particle is proportional to
A. 𝑣 2
B. √1 − 𝑣 2 /𝑐 2
C. −𝑚𝑐 2 √1 − 𝑣 2 /𝑐 2
D. 𝑚𝑐 2 (1 − 𝑣 2 /𝑐 2 )
, Answer: C
Rationale: The relativistic action uses proper time, giving this Lagrangian.
4. The dimension of action is
A. Energy
B. Energy × time
C. Momentum
D. Force × time
Answer: B
Rationale: Action has units of joule-seconds, same as angular momentum.
5. A conserved quantity associated with time translation invariance is
A. Momentum
B. Angular momentum
C. Energy
D. Charge
Answer: C
Rationale: Noether’s theorem links time invariance to energy
conservation.
Electrodynamics
6. Gauss’s law in differential form is
A. ∇ ⋅ 𝐄 = 0
B. ∇ × 𝐄 = − ∂𝐁/ ∂𝑡
C. ∇ ⋅ 𝐄 = 𝜌/𝜀0
D. ∇ × 𝐁 = 0
Answer: C
Rationale: Electric field divergence equals charge density over
permittivity.
7. The vector potential gauge freedom implies
A. Physical fields change
B. Only scalar potential matters
, C. Potentials are not unique
D. Magnetic field vanishes
Answer: C
Rationale: Different potentials can give the same electric and magnetic
fields.
8. The Poynting vector represents
A. Energy density
B. Momentum density
C. Energy flux
D. Charge flow
Answer: C
Rationale: 𝐒 = 𝐄 × 𝐇gives energy flow per unit area.
9. Electromagnetic waves in vacuum travel at
A. 1/√𝜇0 𝜀0
B. √𝜇0 𝜀0
C. 𝑐 2
D. 𝜇0 𝜀0
Answer: A
Rationale: Maxwell’s equations predict wave speed 𝑐 = 1/√𝜇0 𝜀0 .
10.The displacement current term ensures conservation of
A. Energy
B. Charge
C. Momentum
D. Mass
Answer: B
Rationale: It guarantees continuity equation consistency.
Quantum Mechanics
