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 series circuit has a resistance of 3 Ω and an inductive reactance of 4 Ω. Its impedance is:
सही उत्तर: क) 5 Ω
Z = √(R² + X_L²) = √(9 + 16) = 5 Ω.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In an AC circuit the rms current is I and the current lags the voltage by φ. The 'wattless' component of the current is:
सही उत्तर: घ) I sin φ
The component I cos φ in phase with the voltage consumes power; the quadrature component I sin φ contributes no average power and is called wattless current.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The rms value of a symmetric square-wave voltage that alternates between +V₀ and −V₀ is:
सही उत्तर: ख) V₀
V² equals V₀² at every instant, so its mean is V₀² and V_rms = V₀.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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At the Earth's magnetic poles, the horizontal component of the Earth's magnetic field is:
सही उत्तर: क) zero
At the magnetic poles the angle of dip is 90°, so H = B cos 90° = 0 and the field is entirely vertical.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A superconductor expels magnetic field lines from its interior when cooled below its critical temperature. This is called the:
सही उत्तर: ग) Meissner effect
The Meissner effect shows that a superconductor behaves as a perfect diamagnet (B = 0 inside).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A charged particle moves through a region containing only a uniform magnetic field. Which quantity remains constant?
सही उत्तर: घ) its speed (kinetic energy)
The magnetic force is always perpendicular to the velocity, so it does no work; the speed and kinetic energy stay constant while the direction changes.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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According to the Biot–Savart law, the magnetic field dB due to a current element I dl at a point at distance r (θ = angle between dl and r) is proportional to:
सही उत्तर: घ) I dl sin θ / r²
dB = (μ₀/4π) I dl sin θ / r², so it varies as the sine of the angle and inversely as the square of the distance.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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As the temperature of a pure semiconductor such as silicon is raised, its electrical resistance:
सही उत्तर: ग) decreases
Heating breaks more covalent bonds and creates more electron–hole pairs, so conductivity rises and resistance falls (negative temperature coefficient).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The number of electrons passing through a cross-section of a wire per second when it carries a current of 1 A is about:
सही उत्तर: ख) 6.25 × 10¹⁸
n = I/e = 1/(1.6 × 10⁻¹⁹) ≈ 6.25 × 10¹⁸ electrons per second.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A uniform wire of resistance R is bent into an equilateral triangle. The resistance between any two of its corners is:
सही उत्तर: क) 2R/9
Each side has R/3; between two corners one side (R/3) is in parallel with the other two (2R/3): (R/3 × 2R/3)/R = 2R/9.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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