Question 1

Semiconductor devices: Why are suitable impurities (dopants) intentionally added to a pure semiconductor?  State the primary objective of doping for electronic applications (diodes, transistors, ICs).  Choose the correct option.

Accepted Answer

ConceptDoping introduces donor (n-type) or acceptor (p-type) atoms, raising electron or hole concentration. This lowers resistivity and enables controllable junction behavior.ResultDevices rely on engineered carrier profiles (pn junctions, MOSFET channels).Final AnswerTo increase its electrical conductivity by increasing free carriers (form n-type or p-type)

Question 2

Hydrostatics: Under which condition will a siphon fail to operate?  Assume a standard siphon transferring liquid from a higher container to a lower one through a tube arching over the rim.  Choose the correct option.

Accepted Answer

ConceptA siphon works because a continuous liquid column is sustained, with atmospheric pressure plus gravity maintaining flow from higher to lower level. Classic analysis uses atmospheric pressure to start and sustain the column over the crest.ReasoningIn vacuum, the pressure support is absent and vapor cavities form, breaking the column; practical siphons fail. (Additionally, if both levels are the same or the crest exceeds barometric height for the liquid, siphoning fails.)Final AnswerIn a vacuum, where atmospheric pressure is absent

Question 3

Isotopes: What do atoms of the same element (isotopes) have in common?  Focus on nuclear composition and atomic number vs. mass number for isotopic nuclides.  Choose the correct option.

Accepted Answer

ConceptIsotopes: same Z (protons), different N (neutrons) ⇒ different mass number A = Z + N.ExampleCarbon-12 and Carbon-14 both have Z = 6 but N = 6 and 8 respectively.Final AnswerThe same number of protons (atomic number) but different neutrons

Question 4

Acoustics: Order of increasing speed of sound across media  Considering typical room conditions, arrange media so that the velocity of sound increases in the correct order from least to greatest.  Choose the correct option.

Accepted Answer

ConceptSound speed increases with bulk modulus and decreases with density; generally vgas liquid solid.Typical valuesAir ≈ 343 m/s; Water ≈ 1500 m/s; Steel ≈ 5000 m/s.Final AnswerAir, Water, Steel

Question 5

Sound intensity: What is the correct physical unit for intensity of sound?  Recall that intensity is acoustic power transmitted per unit area, not a subjective level measure.  Choose the correct option.

Accepted Answer

Concept & formulaIntensity I = Power/Area ⇒ SI unit W/m².ClarificationDecibel (dB) is a logarithmic level (ratio) unit for intensity or pressure levels, not the base SI unit of intensity itself.Final AnswerWatt per square metre (W/m²)

Question 6

Astronomical measures: A light-year is a unit of what physical quantity?  Definition applies to distances in interstellar/galactic scales.  Choose the correct option.

Accepted Answer

DefinitionLight-year = distance light travels in vacuum in one Julian year.ReasoningDespite the name, it is a measure of distance, not time.Final AnswerDistance

Question 7

Optics and media: In which medium does light travel at the maximum speed?  Assume standard, non-dispersive comparison among common media.  Choose the correct option.

Accepted Answer

ConceptSpeed of light c is maximal in vacuum; in media v = c/n with refractive index n ≥ 1.Final AnswerVacuum

Question 8

Boiling and altitude: Why does cooking take longer in the hills than in the plains?  Assume open-vessel boiling and typical high-altitude atmospheric conditions.  Choose the correct option.

Accepted Answer

ConceptBoiling point decreases with pressure. At higher altitudes, atmospheric pressure is lower, so water boils below 100°C.EffectSince the maximum attainable cooking temperature (boiling) is lower, food takes longer to cook.Final AnswerLower atmospheric pressure lowers water's boiling point, so cooking temperature is reduced

Question 9

Thermal sensation vs. temperature: Why does a metal pen cap feel colder than its plastic body at the same room temperature (15°C)?  Explain the sensory reason though both parts are at 15°C in equilibrium.  Choose the correct option.

Accepted Answer

ConceptSensation of cold/warmth depends on heat flow rate. Metals conduct heat away from skin quickly; plastics are poor conductors.ResultGreater heat flux to the metal lowers skin temperature faster, producing a colder sensation even at the same thermometer temperature.Final AnswerMetal has much higher thermal conductivity and draws heat from your skin faster

Question 10

Dimensional formula identification: ML²T⁻² corresponds to which physical quantity?  Use standard M–L–T dimensional analysis for mechanical quantities.  Choose the correct option.

Accepted Answer

DerivationWork = Force × distance = (MLT-2) × L = ML2T-2.Torque = r × F has the same dimensions ML2T-2.ContrastPower = Work/time ⇒ ML2T-3; Momentum = MLT-1; Pressure = ML-1T-2.Final AnswerWork or energy (also torque)

Question 11

Dimensional analysis MCQ: Pick the pair whose quantities do NOT have identical dimensions.  Compare each pair using M–L–T dimensional formulae and identify the mismatch.  Choose the correct option.

Accepted Answer

Check each pairForce vs weight ⇒ both MLT-2.Pressure vs stress ⇒ both ML-1T-2.Angular momentum vs Planck's constant ⇒ both ML2T-1.Power vs torque ⇒ ML2T-3 vs ML2T-2 (different).Final AnswerPower and torque

Question 12

Astronomical instruments: What do large astronomical telescopes use as the objective?  Consider modern observatory-class instruments designed for faint, distant objects.  Choose the correct option.

Accepted Answer

ConceptReflecting telescopes use large concave mirrors: lighter for large apertures, no chromatic aberration, easier support from behind.Final AnswerConcave mirror (reflector)

Question 13

Thermometry: Why is mercury commonly used as a thermometric liquid instead of water?  Select the most appropriate combined reason relevant to laboratory/clinical thermometers.  Choose the correct option.

Accepted Answer

ReasonsMercury shows near-uniform thermal expansion, does not wet glass (clear meniscus/readings), and boils at ~357°C enabling a wide upper range. It is also opaque and shiny for easy visibility.NoteAlthough mercury freezes at about −39°C (higher than alcohols), its other properties make it favorable for many thermometers.Final AnswerIt expands uniformly, does not wet glass, and has a high boiling point giving a wide measurable range

Question 14

Flight regimes: A supersonic aircraft flies at what relative speed?  Describe its speed in relation to the local speed of sound (Mach number concept).  Choose the correct option.

Accepted Answer

DefinitionSupersonic: Mach number > 1, i.e., aircraft speed exceeds local speed of sound (≈ 343 m/s at sea level, 20°C).Final AnswerGreater than the speed of sound (Mach > 1)

Question 15

Materials in appliances: Why is mica used inside devices such as electric irons and toasters?  Identify the key property that makes mica suitable as spacers/insulators near hot elements.  Choose the correct option.

Accepted Answer

ConceptMica is a sheet silicate with excellent electrical insulation, high dielectric strength, and thermal stability, ideal near heating coils.Final AnswerIt is a good electrical insulator with high heat resistance (high dielectric strength)

Question 16

Waveguides and communication: On which optical principle do fibre-optic cables operate?  Consider total internal reflection vs. other wave phenomena inside a high-index core and lower-index cladding.  Choose the correct option.

Accepted Answer

ConceptLight launched at angles below the critical angle reflects entirely at the core–cladding boundary (ncore > nclad), guiding signals over long distances.Final AnswerTotal internal reflection within the core–cladding structure

Question 17

SI units: Identify what 'lux' measures.  Lux is defined as luminous flux incident per unit area in photometry; it quantifies how brightly a surface is illuminated. Choose the correct option.

Accepted Answer

Given dataUnit mentioned: lux.ConceptIn SI, lux (lx) is the unit of illuminance, equal to 1 lumen per square metre (1 lx = 1 lm·m−2).Common pitfallsConfusing illuminance (lux) with luminous intensity (candela) or luminous flux (lumen).Final AnswerIlluminance (luminous flux per unit area)

Question 18

Vectors vs. scalars: Pick the scalar quantity from the list.  A scalar has magnitude only; a vector has both magnitude and direction. Choose the correct option.

Accepted Answer

ConceptScalars: magnitude only (e.g., work, energy, temperature).Vectors: magnitude + direction (e.g., velocity, acceleration, force).ReasoningAmong the options, work is a scalar; the others are vectors.Final AnswerWork

Question 19

Railway engineering and circular motion: Why tracks are banked on curves?  Banking reduces reliance on lateral friction and safely provides the centripetal force for turning at speed. Choose the correct option.

Accepted Answer

ConceptOn curves, a component of the normal reaction from a banked track supplies part/all of the required centripetal force.This allows higher safe speeds without excessive side friction or risk of derailment.Final AnswerTo provide the necessary centripetal force (reduce lateral friction needs)

Question 20

Capillarity with a too-short tube: What happens to the water rise?  If a thin capillary tube is replaced by another tube of insufficient length compared with the predicted capillary rise, predict the observed behavior. Choose the correct option.

Accepted Answer

ConceptCapillary rise height h is set by surface tension, density, gravity, and radius.If tube length Final AnswerWater rises to the top and overflows (spills)

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