Question 1

A flat plate is moving normal to its plane through a gas under the action of a constant force F. The gas is kept at very low pressure. The speed of the plate v is much less than the average speed u of the gas molecules. Which of the following option…

Accepted Answer

n = number of molecules per unit volume u = average speed of gas molecules When the plate is moving with speed v, the relative speed of molecules w.r.t. leading force = v + u Coming head-on, momentum transformed to plate per collision = 2m(u + v) Number of collision in time: Δt = ((v + v0)nΔtA)/2 where A = Surface area So, momentum transferred in time Δt = m(u + v)2nAΔt from front surface Similarly momentum transferred in time = m(u – v)2nAΔt from back surface Net force = mnA[(v + u)2 – (u – v)2] = mnA[4vu] F ∝ v Pleading– Ptrailing = mn[u + v]2 – mn[u – v]2 = mn[4uv] = 4mnuv ΔP ∝ uv

Question 2

Newtonian impulse concept: Equal force applied for equal time on different masses. Two bodies of different masses, both initially at rest, are acted upon by the same constant force for the same duration. What common physical quantity do they acquire…

Accepted Answer

Given data Initial state: both at rest. Same force F acts for the same time t. Concept/ApproachImpulse–momentum theorem: Impulse = F·t = change in momentum. Step-by-stepImpulse on body 1 = F·t; impulse on body 2 = F·t (same).Since both start from rest, final momentum of each = F·t. Common pitfallsAcceleration depends on mass (a = F/m), so not equal; velocities and kinetic energies also differ. Final AnswerEqual change in momentum (same momentum after push)

Question 3

Metric units: Convert microns (micrometres) to millimetres. One thousand microns (μm) is equal to how many millimetres (mm)? Choose the correct option.

Accepted Answer

Given data 1 μm = 10-6 m. 1 mm = 10-3 m. Calculation1000 μm = 1000 × 10-6 m = 10-3 m = 1 mm. Final Answer1 millimetre

Question 4

Everyday physics: Why blotting paper absorbs ink. The absorption of liquid ink into blotting paper occurs due to which physical effect in porous materials? Choose the correct option.

Accepted Answer

Given data Porous paper absorbs ink spontaneously. ConceptIn narrow pores, surface tension and adhesion create capillary rise, drawing liquid into the material. Final AnswerCapillary action (capillarity)

Question 5

Nature of sound in air: Wave classification. Sound waves traveling through air belong to which category of waves by particle motion and medium requirement? Choose the correct option.

Accepted Answer

Concept Sound in air requires a medium → mechanical wave. Air particles oscillate parallel to propagation → longitudinal. Final AnswerLongitudinal mechanical waves

Question 6

Magnetism of a bar magnet: Field strength at the center. Compared to its poles, the magnetic field at the geometric center of a uniformly magnetized bar magnet is what? Choose the correct option.

Accepted Answer

Concept Magnetic field lines crowd at poles (strongest near ends). At the mid-point (center), contributions largely cancel → weakest field. Final AnswerMinimum (approximately zero)

Question 7

Wave properties: Which property is independent of the others? For a traveling wave, velocity v = fλ relates speed, frequency, and wavelength. Which property does not depend on that relation? Choose the correc…

Accepted Answer

Concept Dispersion relation: v = fλ ties v, f, and λ. Amplitude is independent of that relation (it affects energy/intensity, not basic kinematic linkage). Final AnswerAmplitude

Question 8

Friction and walking: Sand vs. concrete. Why is it more difficult to walk on a sandy surface than on a rigid concrete road under the same conditions? Choose the correct option.

Accepted Answer

Concept Static friction ∝ normal reaction × coefficient of friction. On sand, the surface deforms and shifts, reducing effective normal reaction and reliable contact, so available friction is less. Final AnswerSand yields, reducing normal reaction and friction

Question 9

Nuclear scales: Unit for nuclear sizes. In nuclear physics, typical nuclear radii are expressed using which specialized unit? Choose the correct option.

Accepted Answer

Concept Nuclear radii ~ a few femtometres. Final AnswerFermi (femtometre, 1 fm = 10⁻¹⁵ m)

Question 10

Boiling point under different locations: Pressure cooker with valve open. Of the locations listed in the options, a pressure cooker operated with the pressure valve open will attain its highest inside temperature at which location? Choose the correc…

Accepted Answer

Kolkata (near sea level)

Question 11

Nobel Prize in Physics (1930): C. V. Raman’s discovery. Sir C. V. Raman received the Nobel Prize for his work on which radiation-related phenomenon, involving inelastic scattering and wavelength shift? Choose the correct option.

Accepted Answer

Concept Raman observed frequency/wavelength shifts when light scatters in matter → Raman effect. Final AnswerRaman effect (inelastic scattering of light)

Question 12

Stellar astronomy: Stars that appear single but are double in a telescope. What are stars called that look single to the naked eye yet resolve into two components when viewed through a telescope? Choose the correct option.

Accepted Answer

Concept Binary or double stars are two stars gravitationally bound that may appear as one to unaided vision. Final AnswerBinary (double) stars

Question 13

Radioactivity: Which emission is not characteristic of ordinary radioactive decay? From the types listed, identify the one not typically emitted in standard (natural) radioactive decay chains. Choose the correct option.

Accepted Answer

Concept Natural radioactive decays commonly emit α, β, and γ radiation. Free neutron emission is not typical of standard natural decays (more common in fission events). Final AnswerNeutrons

Question 14

Vector vs. scalar: Identify the vector quantity. Which of the following physical quantities has both magnitude and direction (i.e., is a vector)? Choose the correct option.

Accepted Answer

Concept Vectors have magnitude and direction. Momentum (p = m·v) is a vector; work, energy, and speed are scalars. Final AnswerMomentum

Question 15

Everyday capillarity: Why oil rises in a lamp wick. Oil rises up a lamp’s cotton wick primarily due to which physical principle in fine capillaries? Choose the correct option.

Accepted Answer

Concept In narrow pores, surface tension and adhesion to fibers draw liquid upwards → capillarity. Final AnswerCapillary action (surface tension with adhesion)

Question 16

Energy units: Convert watt-hour to joules. One watt-hour represents the energy expended by 1 watt sustained for 1 hour. What is this energy in joules? Choose the correct option.

Accepted Answer

Given 1 W = 1 J·s⁻¹ 1 hour = 3600 s CalculationEnergy = Power × Time = 1 J·s⁻¹ × 3600 s = 3600 J. Check1 kWh = 1000 W × 3600 s = 3.6 × 106 J (so 1 Wh = 3.6 × 103 J). Final Answer3600 J

Question 17

Dimensional analysis MCQ: Identify the pair of physical quantities that do not share identical dimensions.  Out of the following pairs, determine which pair has different dimensional formula; assume standard M–L–T system for mechanics quantities.  C…

Accepted Answer

Given data We compare dimensions of four pairs under the M–L–T system. Concept/ApproachUse dimensional formulae: Force = MLT-2; Work/Energy = ML2T-2; Power = ML2T-3; Impulse = change of momentum = MLT-1; Pressure/Stress = ML-1T-2; Torque (moment of force) = ML2T-2. Step-by-step checkWork vs torque ⇒ both ML2T-2 (identical).Impulse vs momentum ⇒ both MLT-1 (identical).Pressure vs stress ⇒ both ML-1T-2 (identical).Power vs energy ⇒ ML2T-3 vs ML2T-2 (different). Common pitfallsConfusing torque with power; torque shares dimensions with work/energy, but power includes per-unit-time. Final AnswerPower and energy

Question 18

Applications of radioisotopes: What does the radiocarbon (C-14) dating technique estimate?  Choose the most appropriate target material that C-14 dating is designed to age-date in archaeology and geology.  Choose the correct option.

Accepted Answer

Given data Technique: Radiocarbon dating (C-14). Concept/ApproachC-14 is produced in the atmosphere and incorporated into living organisms. After death, C-14 decays (half-life ≈ 5730 years). Measuring the C-14/C-12 ratio estimates age. Key pointsApplicable materials: organic remains (wood, charcoal, bone, cloth, paper) up to ~50,000 years.Not suitable for igneous rocks or pure metals without organic carbon. Final AnswerAncient wooden artifacts, bones, or other once-living organic remains

Question 19

Astronomy and light travel time: How long does sunlight take to reach Earth?  Give the approximate time delay for light traveling from the Sun to Earth's surface under average conditions.  Choose the correct option.

Accepted Answer

Given Average Earth–Sun distance ≈ 1 astronomical unit (1 AU) ≈ 1.496 × 1011 m. Speed of light c ≈ 3.00 × 108 m/s. CalculationTime = Distance / Speed = (1.496 × 1011) / (3.00 × 108) s ≈ 498.7 s.498.7 s ≈ 8 minutes 18.7 seconds (commonly rounded to ≈ 8 min 20 s). Final AnswerAbout 8 minutes 20 seconds

Question 20

Optical phenomena in the atmosphere: What physical principle best explains a desert mirage?  Consider the shimmering water-like appearance on hot roads or deserts caused by vertical temperature gradients in air.  Choose the correct option.

Accepted Answer

ConceptNear hot surfaces, air is hotter and less dense close to the ground; refractive index decreases with height, creating layers. Light from the sky bends continuously and can undergo effective total internal reflection, reaching the eye from below, mimicking water. Key ideaMirage = apparent inverted image due to refraction approaching total internal reflection in a refractive-index gradient. Final AnswerTotal internal reflection in stratified hot air

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