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NEET Practice: Physics 6
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1.
The acceleration due to gravity at a height h above Earth's surface is g' = g(1 - 2h/R). For h = R/2, g' is:
(a) g/2
(b) g/3
(c) g/4
(d) g/9
Show Answer & Explanation
Correct Answer: (d) g/9
Explanation:
g' = g / (1 + h/R)² = g / (1.5)² = g / 2.25 = (4/9)g
2.
The wavelength of light in vacuum is 6000 Å. Its wavelength in a medium of refractive index 1.5 is:
(a) 4000 Å
(b) 6000 Å
(c) 9000 Å
(d) 3000 Å
Show Answer & Explanation
Correct Answer: (a) 4000 Å
Explanation:
λ_medium = λ_vacuum / μ = 6000 / 1.5 = 4000 Å
3.
The self-inductance of a coil is 2 H. The energy stored when current 2 A flows through it is:
(a) 2 J
(b) 4 J
(c) 8 J
(d) 1 J
Show Answer & Explanation
Correct Answer: (b) 4 J
Explanation:
Energy = (1/2)LI² = (1/2)×2×4 = 4 J
4.
The rate of heat flow through a rod is Q. If length is doubled and area halved, new rate is:
(a) Q/4
(b) Q/2
(c) Q
(d) 2Q
Show Answer & Explanation
Correct Answer: (a) Q/4
Explanation:
Rate ∝ A/L → new rate = Q × (A/2) / (2L) = Q/4
5.
The pH of a solution is 3. The hydrogen ion concentration is:
(a) 10⁻³ mol/L
(b) 10³ mol/L
(c) 0.001 mol/L
(d) Both (a) and (c)
Show Answer & Explanation
Correct Answer: (d) Both (a) and (c)
Explanation:
pH = -log[H⁺] → [H⁺] = 10⁻³ mol/L = 0.001 mol/L
6.
A convex lens of focal length 20 cm forms an image at 30 cm. The object distance is:
(a) 60 cm
(b) 12 cm
(c) 60 cm (virtual)
(d) 12 cm (virtual)
Show Answer & Explanation
Correct Answer: (a) 60 cm
Explanation:
1/f = 1/v - 1/u → 1/20 = 1/30 - 1/u → u = -60 cm (real object)
7.
The rms speed of gas molecules is v. If temperature is doubled, rms speed becomes:
(a) v
(b) √2 v
(c) 2v
(d) 4v
Show Answer & Explanation
Correct Answer: (b) √2 v
Explanation:
v_rms ∝ √T → temperature doubled → speed increases by √2
8.
The number of neutrons in ¹⁴C is:
(a) 6
(b) 8
(c) 14
(d) 20
Show Answer & Explanation
Correct Answer: (b) 8
Explanation:
Mass number 14, atomic number 6 → neutrons = 14 - 6 = 8
9.
The torque on a bar magnet in a uniform magnetic field is maximum when angle between M and B is:
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Show Answer & Explanation
Correct Answer: (c) 90°
Explanation:
τ = MB sinθ → maximum when sinθ = 1 (θ = 90°)
10.
The dimensional formula of Planck’s constant is:
(a) [ML²T⁻¹]
(b) [ML ²T⁻²]
(c) [M ²L²T⁻¹]
(d) [MLT⁻¹]
Show Answer & Explanation
Correct Answer: (a) [ML²T⁻¹]
Explanation:
E = hν → h = E/ν → [ML²T⁻ ²] / [T⁻¹] = [ML ²T⁻¹]