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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In Young's double-slit experiment the slits are 1.2 mm apart and the screen is 1 m away. If the fringe width is 0.5 mm, the wavelength of the light is:
सही उत्तर: ख) 600 nm
λ = βd/D = 0.5 × 10⁻³ × 1.2 × 10⁻³/1 = 6 × 10⁻⁷ m.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A ray in water (n = 4/3) strikes a water–glass (n = 3/2) boundary at an angle of incidence of 30°. The sine of the angle of refraction is:
सही उत्तर: क) 4/9
n₁ sin i = n₂ sin r: (4/3)(1/2) = (3/2) sin r, so sin r = 4/9.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The critical angle for light going from glass of refractive index 1.5 into air is about:
सही उत्तर: ख) 41.8°
sin C = 1/n = 2/3, so C ≈ 41.8°.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A thin glass lens (n = 1.5) has a focal length f in air. When immersed in a liquid of refractive index 1.25, its focal length becomes:
सही उत्तर: ग) 2.5f
f_liquid/f_air = (1.5 − 1)/(1.5/1.25 − 1) = 0.5/0.2 = 2.5.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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What is the focal length in air of a double-concave glass lens (n = 1.5) whose two surfaces each have a 20 cm radius of curvature?
सही उत्तर: घ) −20 cm
1/f = (1.5 − 1)(−1/20 − 1/20) = −0.05, so f = −20 cm.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An object is placed 15 cm from a convex lens of focal length 10 cm. The magnification produced is:
सही उत्तर: ख) −2
1/v = 1/10 − 1/15 = 1/30 gives v = 30 cm, so m = v/u = 30/(−15) = −2 (real, inverted).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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When an object lies between the pole and the focus of a concave mirror, 10 cm from a mirror of focal length 20 cm, the image formed is:
सही उत्तर: घ) virtual, erect and twice the size of the object
1/v = 1/f − 1/u = −1/20 + 1/10 = 1/20 (Cartesian), so v = +20 cm behind the mirror and m = −v/u = 2: virtual, erect, magnified.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The speed of sound in air at 0 °C is 332 m/s. Its speed at 91 °C is about:
सही उत्तर: क) 383 m/s
v ∝ √T: v = 332 × √(364/273) ≈ 332 × 1.155 ≈ 383 m/s.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A siren of 660 Hz recedes from a listener at rest with a speed of 30 m/s. Taking the speed of sound as 330 m/s, the listener hears a pitch of:
सही उत्तर: ग) 605 Hz
f′ = f v/(v + v_s) = 660 × 330/360 = 605 Hz.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A string 0.6 m long, fixed at both ends, carries waves at 240 m/s. The frequency of its third harmonic is:
सही उत्तर: घ) 600 Hz
fₙ = nv/2L = 3 × 240/1.2 = 600 Hz.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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