भौतिक विज्ञान (Physics) – Physics MCQ
भौतिक विज्ञान (Physics) – CEE प्रवेश
Physics · Medical Entrance (CEE) – Physics, Chemistry, Biology & MAT · ४०७ प्रश्न
४०७ 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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The coefficients of linear (α), superficial (β) and cubical (γ) expansion of a solid are related as:
सही उत्तर: घ) α : β : γ = 1 : 2 : 3
For isotropic solids β = 2α and γ = 3α, giving 1 : 2 : 3. This follows because area involves two dimensions and volume three.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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If the input AC frequency to a full-wave rectifier is 50 Hz, the frequency of the output ripple is:
सही उत्तर: ग) 100 Hz
A full-wave rectifier conducts in both halves of each cycle, so the output pulses occur at twice the input frequency. A half-wave rectifier's output frequency equals the input, 50 Hz.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A Zener diode is commonly used as a:
सही उत्तर: ख) Voltage regulator
Operated in reverse breakdown, a Zener diode keeps the voltage across it nearly constant over a wide range of current. Ordinary p-n diodes are used as rectifiers.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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When a p-n junction diode is forward biased, the width of the depletion layer:
सही उत्तर: क) Decreases
Forward bias opposes the barrier potential, pushing majority carriers into the junction and narrowing the depletion region. Reverse bias widens it.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An n-type semiconductor is obtained by doping silicon with:
सही उत्तर: घ) Phosphorus
Phosphorus is pentavalent; its fifth valence electron becomes a free charge carrier. Trivalent impurities like boron, aluminium and gallium produce p-type semiconductors.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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1 atomic mass unit (u) is equivalent to an energy of approximately:
सही उत्तर: ग) 931.5 MeV
From E = mc², 1 u ≈ 931.5 MeV. 0.511 MeV is the rest energy of an electron.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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When a nucleus emits an alpha particle, its mass number and atomic number respectively:
सही उत्तर: ख) Decrease by 4 and by 2
An alpha particle is a helium nucleus (⁴₂He), so A drops by 4 and Z by 2; e.g. ²³⁸U → ²³⁴Th. The reverse pairing (2 and 4) is a common mix-up.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In β⁻ (beta-minus) decay, the atomic number of the nucleus:
सही उत्तर: क) Increases by 1
A neutron converts into a proton, emitting an electron and an antineutrino, so Z increases by 1 while A is unchanged. In β⁺ decay Z decreases by 1.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The ratio of the radius of the second Bohr orbit to that of the first orbit in a hydrogen atom is:
सही उत्तर: घ) 4 : 1
rₙ ∝ n², so r₂/r₁ = 2²/1² = 4. 2:1 would be true only if r were proportional to n.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The Lyman series of the hydrogen spectrum lies in the:
सही उत्तर: ग) Ultraviolet region
Lyman lines are transitions ending on n = 1, which have large energies and fall in the ultraviolet. The Balmer series (ending on n = 2) lies in the visible region.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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