भौतिक विज्ञान (Physics) – Physics MCQ
भौतिक विज्ञान (Physics) – इन्जिनियरिङ प्रवेश
Physics · Engineering Entrance – Mathematics, Physics, Chemistry & English · १,३९८ प्रश्न
१,३९८ प्रश्न उपलब्ध। मोड छान्नुहोस्:
भौतिक विज्ञान (Physics): प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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A dielectric slab (K = 2) of thickness d/2 is inserted between the plates of a parallel-plate capacitor of separation d and capacitance C₀. The new capacitance is:
सही उत्तर: घ) 4C₀/3
C = ε₀A/(d − t + t/K) = ε₀A/(d/2 + d/4) = (4/3)ε₀A/d = 4C₀/3.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A 2 μF capacitor charged to 100 V and a 4 μF capacitor charged to 50 V are connected in parallel with like plates joined. The common potential is:
सही उत्तर: क) 200/3 V
V = (C₁V₁ + C₂V₂)/(C₁ + C₂) = (200 + 200) μC/6 μF = 66.7 V.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An electron starts from rest and moves 5 cm along a uniform electric field of strength 2000 V/m (in the direction it is pushed). Its kinetic energy gained is:
सही उत्तर: ख) 100 eV
ΔV = Ed = 2000 × 0.05 = 100 V, so the electron gains eΔV = 100 eV.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An electric dipole of moment 2 × 10⁻⁸ C m makes an angle of 30° with a uniform field of 10⁴ N/C. The torque on it is:
सही उत्तर: ख) 10⁻⁴ N m
τ = pE sin θ = 2 × 10⁻⁸ × 10⁴ × 0.5 = 10⁻⁴ N m.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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At a certain distance from a point charge the potential is 600 V and the field is 200 V/m. The distance and the charge are:
सही उत्तर: क) 3 m and 0.2 μC
E = V/r ⇒ r = 600/200 = 3 m; q = Vr/k = 600 × 3/(9 × 10⁹) = 2 × 10⁻⁷ C = 0.2 μC.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Three charges of +1 μC each are at the corners of an equilateral triangle of side 1 m. The magnitude of the net force on any one of them is about (1/4πε₀ = 9 × 10⁹ N m²/C²):
सही उत्तर: घ) 1.56 × 10⁻² N
Each pair force is 9 × 10⁻³ N and the two forces are at 60°: F = 2F₀cos 30° = √3 × 9 × 10⁻³ ≈ 1.56 × 10⁻² N.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A compound microscope has objective focal length 1 cm and eyepiece focal length 5 cm, with a tube length of 15 cm. Its approximate magnifying power for final image at infinity is (D = 25 cm):
सही उत्तर: ग) 75
M ≈ (L/fₒ)(D/fₑ) = (15/1)(25/5) = 75.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A convex lens and a concave lens, each of focal length 25 cm in magnitude, are placed in contact. The combination behaves as:
सही उत्तर: ग) a plane glass plate of zero power
P = 1/f₁ + 1/f₂ = 4 D − 4 D = 0, so the focal length is infinite: the pair acts like a plane plate.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In Young's experiment with λ = 600 nm, a thin glass sheet (n = 1.5) of thickness 6 μm is placed over one slit. The central fringe shifts by:
सही उत्तर: क) 5 fringe widths
Number of fringes shifted = (n − 1)t/λ = 0.5 × 6 × 10⁻⁶/(6 × 10⁻⁷) = 5.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In Young's double-slit experiment the maximum intensity is I₀. At a point where the path difference is λ/3, the intensity is:
सही उत्तर: घ) I₀/4
Phase difference φ = 2π/3, and I = I₀cos²(φ/2) = I₀cos²60° = I₀/4.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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