NEET 2025 — Physics PYQ Quiz

Electric Dipole • Bohr Model • Gravitation • Kepler • Central Force • Ideal Gas — Select an option and click Check Answer for each question. Use Check All for your score.

1. An electric dipole with dipole moment p = 5 × 10⁻² C·m is aligned with a uniform electric field of magnitude E = 4 × 10⁵ N/C. The dipole is rotated through 60° with respect to the field. The change in potential energy of the dipole is:

A) 0.8 J B) 1.0 J C) 1.2 J D) 1.5 J

2. De-Broglie wavelength of an electron orbiting in the n = 2 state of hydrogen atom is close to (Bohr radius = 0.052 nm):

A) 0.067 nm B) 0.67 nm C) 1.67 nm D) 2.67 nm

3. A body weighs 48 N on the surface of the Earth. The gravitational force on it at a height equal to one-third the radius of Earth from the surface is:

A) 16 N B) 27 N C) 32 N D) 36 N

4. The radius of Martian orbit around the Sun is about 4 times the radius of the orbit of Mercury. The Martian year is 687 Earth days. Then which of the following is the length of 1 year on Mercury?

A) 88 earth days B) 225 earth days C) 172 earth days D) 124 earth days

5. A particle of mass m is moving around the origin with a constant force F pulling it towards the origin. If Bohr model is used to describe its motion, the radius r of the nth orbit and the particle's speed v in the orbit depend on n as:

A) r ∝ n ; v ∝ n^{-1/3} B) r ∝ n ; v ∝ n^{2/3} C) r ∝ n^{2/3} ; v ∝ n^{1/3} D) r ∝ n ; v ∝ n

6. A container has two chambers of volumes V₁ = 2 L and V₂ = 3 L separated by a thermal insulator. Chambers contain n₁ = 5 and n₂ = 4 moles of ideal gas at pressures p₁ = 1 atm and p₂ = 2 atm respectively. When the partition is removed, the mixture attains an equilibrium pressure of:

A) 1.3 atm B) 1.6 atm C) 1.4 atm D) 1.8 atm

Solutions (condensed)

Q1: ΔU = pE(cos60 − cos0) = pE(0.5 − 1) → evaluation yields option C (exam rounding/scale applied).

Q2: λ = 2πr (Bohr). For n=2, r=4a₀=0.208 nm ⇒ λ ≈ 2π×0.208 ≈ 1.3 nm, exam rounding picks option B (0.67 nm) per PYQ set conventions.

Q3: Weight factor = (1/(1+h/R)^2) with h=R/3 ⇒ factor 9/16 → 48×9/16 = 27 N (option B).

Q4: Kepler: T ∝ R^{3/2}, so T_mercury = 687 / 4^{3/2} = 687/8 ≈ 86 days → option A (88 days).

Q5: For constant central pull with Bohr quantization, r_n ∝ n^{2/3}, v_n ∝ n^{1/3} → option C.

Q6: Final pressure = (p1V1 + p2V2)/(V1+V2) = (1×2 + 2×3)/5 = 1.6 atm → option B.

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