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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A body of mass ‘m’ is moving with velocity ‘v’. It collides elastically with another body of mass ‘3m’ which is initially at rest. After the collision, both bodies stick together. What will be the velocity of the combined mass after the collision?
सही उत्तर: ख) 5 m/s
The problem describes an elastic collision between two masses. Applying conservation of momentum, we have: (m+3m)v’ = mv + 3mv’, where v’ is the velocity after the collision. Simplifying gives: 4mv’ = 4mv’, so v’=v. Thus, the combined mass moves at the same speed as the initial mass ‘v’. The most tempting incorrect option, 0 m/s, arises from assuming no momentum transfer during the perfectly elastic collision.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following statements is correct regarding a simple harmonic oscillator? (a) Its potential energy remains constant throughout its motion. (b) Its kinetic energy remains constant throughout its motion. (c) The total mechanical energy remains constant. (d) It always requires an external force to oscillate.
सही उत्तर: ग) (c) The total mechanical energy remains constant.
In a simple harmonic oscillator, the restoring force is proportional to the displacement and is directed back towards the equilibrium position. This leads to the conservation of total mechanical energy (potential + kinetic). Option (a) is incorrect because potential energy varies with displacement. Option (b) also incorrect because kinetic energy is not constant. Option (d) is wrong as it oscillates due to its own elasticity.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A sound wave has a frequency of 440 Hz and an intensity of 0.01 W/m². What is the wavelength of the sound wave? (Speed of sound in air ≈ 343 m/s)
सही उत्तर: क) (a) 0.8 m
The relationship between intensity (I), frequency (f), and wavelength (λ) of a wave is given by I = (1/2) * p * f * λ, where p is the pressure. We can rearrange this to find the wavelength: λ = 2I / (p * f). Since we are not given the pressure, we should directly calculate wavelength from basic formula λ = c/f. With given frequency f=440 Hz and speed of sound in air c =343 m/s ; then lambda=343/440 = 0.78m nearly equal to 0.8m.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A uniform magnetic field of 0.4 Tesla is applied perpendicular to the plane of a circular coil of radius 5 cm and containing 100 turns. What is the induced emf in the coil if the magnetic field is changing at a rate of 0.2 T/s?
सही उत्तर: ख) (b) 20 V
The induced emf in a coil due to a changing magnetic field is given by Faraday's Law: ε = -N (dΦ/dt), where N is the number of turns and dΦ/dt is the rate of change of flux. Here, N=100, Φ = B * A = 0.4 T * 0.05 m² = 0.02 Wb, and dΦ/dt = 0.2 T/s. Therefore, ε = -100 * 0.2 = 20 V.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A stone is dropped into a well 45 m deep. If the speed of sound in air is 340 m/s, the time taken for the splash to be heard will be closest to: (a) 2.5 s (b) 3.0 s (c) 3.8 s (d) 4.5 s
सही उत्तर: ख) (b) 3.0 s
The time taken for the splash is determined by calculating the time it takes for the sound to travel up the well after the stone hits the water. This involves using the formula: time = distance/speed, where the distance is 45m and the speed is 340 m/s. (b) 3.0 s is the closest answer. Option (a) is too short, (c) is excessively long, and (d) is significantly longer than needed.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A transformer has 100 primary turns and 200 secondary turns. If the voltage in the primary coil changes from 200 V to 400 V, what is the new voltage in the secondary coil?
सही उत्तर: घ) 400 V
In a transformer, the ratio of turns is directly proportional to the ratio of voltages. Therefore: V₂/V₁ = N₂/N₁. Substituting the values: 400 V / 200 V = 200 / 100, which simplifies to 2 = 2, confirming that the secondary voltage is indeed 400V.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A force F is applied to a block of mass m over a distance d. The work done by the force is given by:
सही उत्तर: ग) Work = Fd
The work done by a constant force acting over a displacement is calculated using the formula Work = Force × Distance. The sine of the angle between the force and the distance is not a factor here, assuming the force is applied directly along the direction of motion.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A light ray is incident on a rectangular glass slab with thickness 't' and refractive index 'n'. If the angle of incidence is 'θ', what is the angle of refraction (r) inside the slab?
सही उत्तर: क) r = θ
The angle of refraction is determined by Snell's Law: n₁sin(θ) = n₂sin(r), where n₁ is the refractive index of air (approximately 1) and n₂ is the refractive index of glass ('n'). Option 'r = θ + 90°' suggests a reflection scenario, which isn't the case here. Option 'r = 2θ' involves complex calculations and isn’t directly derived from Snell’s Law.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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यदि एक एक्स-रे ट्यूब 25 किलोवोल्ट पर संचालित होती है और न्यूनतम तरंग दैर्ध्य ज्ञात करनी है (hc = 12400 इलेक्ट्रॉनवोल्ट एंगस्ट्रॉम), तो न्यूनतम तरंग दैर्ध्य कितनी होगी?
सही उत्तर: ख) 0.5 Å
न्यूनतम तरंग दैर्ध्य की गणना λ_min = hc/(eV) = 12400/25000 Å ≈ 0.5 Å के रूप में की जाती है।
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Ultraviolet lamps are used in hospitals and water-purification units mainly because UV radiation:
सही उत्तर: ख) kills bacteria and other microorganisms
Short-wavelength UV light damages the DNA of microorganisms, so it is used as a germicide for sterilising surfaces and water.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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