NEET UG
- A 250 - Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180^° against the torque is : Answer: 4. 9.1 μ J Key idea: work done in rotating a coil from θ=0 to 180^° is W=MB(cos0-cos180)=2MB , with M=NIA . A=2.1×10⁻²×1.25×10⁻²=2.6... 1
- The ratio of resolving powers of an optical microscope for two wavelengths λ_1 = 4000 and λ_2 = 6000 is : Answer: 2. 3 : 2 Key idea: resolving power of a microscope is ∝dfrac1λ . R₁/R₂=λ₂/λ₁=6000/4000=3/2 , i.e. 3 : 2. 1
- Two Polaroids P_1 and P_2 are placed with their axis perpendicular to each other. Unpolarised light I_0 is incident on P_1. A third polaroid P_3 is kept in between P_1 and P_2 such that its axis makes an angle 45^° with that of P_1. The intensity of… Answer: 2. I₀/8 Key idea: the first polaroid halves unpolarised light; then use Malus's law I=Icos²θ . After P₁ : I₀/2 . After P₃ (45 ^° ):... 1
- A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ,… Answer: 4. y/2x Key idea: when a mirror rotates by θ , the reflected ray turns by 2θ . The spot moves by y=xtan2θ≈2θ x for small angles. So... 1
- A thin prism having refracting angle 10^° is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of seco… Answer: 1. 6 ^° Key idea: dispersion without deviation means the net deviation is zero: (μ₁-1)A₁=(μ₂-1)A₂ . (1.42-1)×10=(1.7-1)A₂⇒ 4.2=0.7A₂... 1
- A spring of force constant k is cut into lengths of ratio 1 : 2 : 3. They are connected in series and the new force constant is k'. Then they are connected in parallel and force constant is k''. Then k' : k'' is : Answer: 2. 1 : 11 Key idea: spring constant is inversely proportional to length. Pieces have lengths L/6,L/3,L/2 , so constants 6k,3k,2k . S... 1
- The two nearest harmonics of a tube closed at one end and open at other end are 220 Hz and 260 Hz. What is the fundamental frequency of the system ? Answer: 1. 20 Hz Key idea: a tube closed at one end has only odd harmonics: f₀,3f₀,5f₀,dots . Consecutive harmonics differ by 2f₀ . 260-220=... 1
- A physical quantity of the dimensions of length that can be formed out of c, G and e^2/4πε_0 is [c is velocity of light, G is universal constant of gravitation and e is charge] : Answer: 4. 1/c²[Ge²/4πε₀]^(1/2) Key idea: match dimensions. e²/4πε₀ is force × length ² : [ML³T⁻²] . G=[M⁻¹L³T⁻²] . Product Ge²/4πε₀=[L⁶T⁻⁴]... 1
- The bulk modulus of a spherical object is 'B'. If it is subjected to uniform pressure 'p', the fractional decrease in radius is : Answer: 3. p/3B Key idea: B=p/Δ V/V , and for a sphere V∝ r³ , so Δ V/V=3Δ r/r . Δ r/r=1/3Δ V/V=p/3B . 1
- A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be : Answer: 3. 1800 Key idea: power radiated P=σ AT⁴∝ r²T⁴ . Radius halved gives factor 1/4 ; temperature doubled gives factor 2⁴=16 . P'=450×1/... 1
- Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities ω_1 and ω_2. They are brought into contact face to face coinciding the axis of rotation. The e… Answer: 1. 1/4 I(ω₁-ω₂)² Key idea: angular momentum is conserved when the discs join. Iω₁+Iω₂=2Iω⇒ω=ω₁+ω₂/2 . Loss =1/2Iω₁²+1/2Iω₂²-1/2(2I)ω... 1
- Which of the following statements are correct ?(a) Centre of mass of a body always coincides with the centre of gravity of the body.(b) Centre of mass of a body is the point at which the total gravitational torque on the body is zero.(c) A couple on… Answer: 4. (b) and (d) Key idea: check each statement. (a) False: centre of mass and centre of gravity coincide only in a uniform gravitatio... 1
- A rope is wound around a hollow cylinder of mass 3 kg and radius 40 cm. What is the angular acceleration of the cylinder if the rope is pulled with a force of 30 N ? Answer: 2. 25 rad/s ² Key idea: τ=Iα , with τ=FR and I=MR² for a hollow cylinder. τ=30×0.4=12 N m, I=3×0.4²=0.48 kg m ² . α=12/0.48=25 rad/s... 1
- Thermodynamic processes are indicated in the following diagram.Match the following :Column-1: P. Process I; Q. Process II; R. Process III; S. Process IVColumn-2: a. Adiabatic; b. Isobaric; c. Isochoric; d. Isothermal Answer: 1. P → c, Q → a, R → d, S → b Key idea: identify each process from the P-V diagram. I: vertical line, volume constant, isochoric (c)... 1
- Zygotic meiosis is characteristic of : Answer: 3. textitChlamydomonas In zygotic meiosis the zygote divides by meiosis first, so the plant body is haploid. This is the haplontic l... 1
- Select the mismatch : Answer: 4. textitPinus - Dioecious The mismatch is Pinus - dioecious. Pinus is monoecious: male and female cones are on the same tree. Cycas... 1
- Which one of the following is related to Ex-situ conservation of threatened animals and plants ? Answer: 4. Wildlife Safari parks Ex-situ conservation protects species outside their natural habitat, for example in zoos, botanical gardens... 1
- Presence of plants arranged into well defined vertical layers depending on their height can be seen best in : Answer: 1. Tropical Rain Forest A tropical rain forest shows the best stratification, with well-defined vertical layers: emergent trees, can... 1
- Plants which produce characteristic pneumatophores and show vivipary belong to : Answer: 1. Halophytes Mangrove plants live in saline, waterlogged soil. They have pneumatophores (breathing roots) and show vivipary (seed g... 1
- Asymptote in a logistic growth curve is obtained when : Answer: 1. K = N In the logistic growth curve the upper asymptote is reached when the population size N equals the carrying capacity K , so... 1
- Which one from those given below is the period for Mendel's hybridization experiments ? Answer: 4. 1856 - 1863 Mendel carried out his hybridization experiments on garden pea from 1856 to 1863. He published the results in 1866. 1
- Which of the following RNAs should be most abundant in animal cell ? Answer: 4. r-RNA Among cellular RNAs, rRNA makes up about 80% of the total RNA, so it is the most abundant. tRNA is about 15%, and mRNA only... 1
- Which statement is wrong for Krebs' cycle ? Answer: 3. The cycle starts with condensation of acetyl group (acetyl CoA) with pyruvic acid to yield citric acid The wrong statement is opt... 1
- Which of the following is made up of dead cells ? Answer: 2. Phellem Phellem (cork) is made of dead cells with suberin deposits in the walls and no protoplasm. Collenchyma, phloem (sieve ele... 1