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 photodiode is normally operated in:
सही उत्तर: ख) reverse bias
In reverse bias the small dark current changes markedly with light intensity, making it suitable for detecting light.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The energy released in the fission of one uranium-235 nucleus is about:
सही उत्तर: घ) 200 MeV
Each U-235 fission releases roughly 200 MeV, most of it as kinetic energy of the fission fragments.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The activity of a radioactive sample falls to 1/16 of its initial value in 80 days. Its half-life is:
सही उत्तर: घ) 20 days
1/16 = (1/2)⁴, so 4 half-lives = 80 days and one half-life = 20 days.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In the Bohr model of the hydrogen atom, the ratio of the speed of the electron in the first orbit to that in the second orbit is:
सही उत्तर: क) 2 : 1
The orbital speed vₙ ∝ 1/n, so v₁ : v₂ = 2 : 1.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An inductor of 2 H is connected in series with a 4 Ω resistor. The time constant of the circuit is:
सही उत्तर: ग) 0.5 s
Time constant of an LR circuit τ = L/R = 2/4 = 0.5 s.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In a series AC circuit containing a resistor and an inductor with R = X_L, the power factor is:
सही उत्तर: क) 1/√2
cos φ = R/Z = R/√(R² + X_L²) = R/(R√2) = 1/√2.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The quality factor (Q-factor) of a series LCR circuit is:
सही उत्तर: घ) (1/R)√(L/C)
Q = ω₀L/R with ω₀ = 1/√(LC), which gives Q = (1/R)√(L/C).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Soft iron is preferred for the cores of electromagnets because it has:
सही उत्तर: ख) high permeability and low retentivity
Soft iron magnetises strongly (high permeability) and loses its magnetism easily when the current stops (low retentivity and coercivity).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The magnetic field at the centre of a semicircular wire of radius r carrying a current I (the straight leads being radial) is:
सही उत्तर: ग) μ₀I/(4r)
A full loop gives μ₀I/(2r); a semicircle gives half of that, μ₀I/(4r), and radial leads contribute nothing at the centre.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A galvanometer of resistance 99 Ω is to be shunted so that only 1% of the main current passes through it. The required shunt resistance is:
सही उत्तर: क) 1 Ω
I_g G = (I − I_g)S, so 0.01I × 99 = 0.99I × S, giving S = 1 Ω.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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