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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Light of wavelength 500 nm falls normally on a diffraction grating having 5000 lines per cm. The sine of the angle of the first-order maximum is:
सही उत्तर: क) 0.25
Grating element d = 1 cm/5000 = 2 × 10⁻⁶ m; d sin θ = λ gives sin θ = 5 × 10⁻⁷/2 × 10⁻⁶ = 0.25.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In Young's double-slit experiment, light of wavelength 600 nm is used with slits 0.3 mm apart. The angular fringe width is:
सही उत्तर: घ) 2 × 10⁻³ rad
Angular fringe width θ = λ/d = 600 × 10⁻⁹/(0.3 × 10⁻³) = 2 × 10⁻³ rad, independent of the screen distance.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Light travels a distance of 4 cm in glass of refractive index 1.5. The equivalent optical path (distance light would travel in vacuum in the same time) is:
सही उत्तर: क) 6 cm
Optical path = n × geometric path = 1.5 × 4 cm = 6 cm.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A Galilean telescope has an objective of focal length 50 cm and an eyepiece (concave lens) of focal length 5 cm. In normal adjustment the distance between the lenses is:
सही उत्तर: ख) 45 cm
In a Galilean telescope the concave eyepiece is placed inside the objective's focus: L = f₀ − |fₑ| = 50 − 5 = 45 cm.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The objective lens of an astronomical telescope should have:
सही उत्तर: घ) a large focal length and a large aperture
A long focal length gives high magnifying power (f₀/fₑ), and a large aperture gathers more light and gives better resolution.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Two coherent light waves, each of intensity I₀, superpose. The maximum resultant intensity is:
सही उत्तर: ग) 4I₀
Amplitudes add at a maximum: (2a)² = 4a², so I_max = 4I₀ (for incoherent sources the intensities simply add to 2I₀).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The wavefront of light from a point source at a finite distance is:
सही उत्तर: ग) spherical
Light spreads equally in all directions from a point source, so points of equal phase lie on spheres centred on the source.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Red light is used for danger signals mainly because red light:
सही उत्तर: घ) is scattered least by the atmosphere
Rayleigh scattering varies as 1/λ⁴, so long-wavelength red light is scattered least and remains visible from far away through fog and dust.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A right-angled isosceles glass prism is used to turn a ray through 90° by total internal reflection at its hypotenuse (angle of incidence 45°). The refractive index of the glass must be greater than:
सही उत्तर: क) √2
TIR needs 45° > critical angle C, i.e. sin C = 1/n < sin 45° = 1/√2, so n > √2 ≈ 1.414.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The minimum length of a vertical plane mirror in which a person of height h can see his full image is:
सही उत्तर: ख) h/2
Rays from the head and feet reach the eye after reflection at points midway in height, so the mirror needs to be only half the person's height.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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