#neet
- A cylinder contains hydrogen gas at pressure of 249 kPa and temperature 27^°C.Its density is : (R = 8.3 J mol^-1 K^-1) Answer: 2. 0.2 kg/m ³ Use the ideal gas equation in density form: P=ρ RT/M . M=2×10⁻³ kg/mol, T=300 K, P=2.49×10⁵ Pa. ρ=PM/RT=frac2.49×10⁵×2... 1
- A ray is incident at an angle of incidence i on one surface of a small angle prism (with angle of prism A) and emerges normally from the opposite surface. If the refractive index of the material of the prism is μ, then the angle of incidence is nearl… Answer: 3. μ A For a small-angle prism, with emergent ray normal to the second face, the angle of refraction at the second face is 0. Since... 1
- Two cylinders A and B of equal capacity are connected to each other via a stop cock. A contains an ideal gas at standard temperature and pressure. B is completely evacuated. The entire system is thermally insulated. The stop cock is suddenly opened.… Answer: 2. adiabatic The system is thermally insulated, so no heat enters or leaves: Q=0 . That makes the process adiabatic. (This is a free... 1
- A body weighs 72 N on the surface of the earth. What is the gravitational force on it, at a height equal to half the radius of the earth ? Answer: 2. 32 N Gravitational force varies as g , and g at height h is g(R/R+h)² . With h=R/2 : (R/1.5R)²=4/9 . F=72×4/9=32\ N Answer: optio... 1
- The solids which have the negative temperature coefficient of resistance are : Answer: 4. insulators and semiconductors Metals have a positive temperature coefficient of resistance: resistance rises with temperature as... 1
- The phase difference between displacement and acceleration of a particle in a simple harmonic motion is : Answer: 1. π rad For SHM, x=Asinω t , and acceleration a=-ω²x . The negative sign means acceleration is always opposite in direction to disp... 1
- A screw gauge has least count of 0.01 mm and there are 50 divisions in its circular scale.The pitch of the screw gauge is : Answer: 3. 0.5 mm Least count =pitch/number of circular divisions . pitch=0.01\ mm×50=0.5\ mm Answer: option 3. 1
- In a guitar, two strings A and B made of same material are slightly out of tune and produce beats of frequency 6 Hz. When tension in B is slightly decreased, the beat frequency increases to 7 Hz. If the frequency of A is 530 Hz, the original frequenc… Answer: 2. 524 Hz Frequency of a string f∝√(T) . Decreasing tension of B lowers its frequency. Beat frequency was 6 Hz and rose to 7 Hz afte... 1
- Two particles of mass 5 kg and 10 kg respectively are attached to the two ends of a rigid rod of length 1 m with negligible mass.The centre of mass of the system from the 5 kg particle is nearly at a distance of : Answer: 3. 67 cm Take the 5 kg mass as the origin. Centre of mass: x_cm=5(0)+10(100)/5+10=1000/15≈67\ cm It lies closer to the heavier mass,... 1
- Find the torque about the origin when a force of 3j N acts on a particle whose position vector is 2k m. Answer: 3. -6i N m Torque vecτ=vec r×vec F . vecτ=2hat k×3hat j=6(hat k×hat j)=6(-hat i)=-6hat i\ N m Since hat j×hat k=hat i , reversing th... 1
- Light with an average flux of 20 W/cm^2 falls on a non-reflecting surface at normal incidence having surface area 20 cm^2. The energy received by the surface during time span of 1 minute is : Answer: 3. 24×10³ J Energy received = flux × area × time. E=20\ W/cm²×20\ cm²×60\ s=24000\ J=24×10³\ J Answer: option 3. 1
- A spherical conductor of radius 10 cm has a charge of 3.2×10^-7 C distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere ?≤ft(1/4πε_0 = 9×10^9\ N m^2/C^2) Answer: 2. 1.28×10⁵ N/C Outside a uniformly charged sphere, the field is the same as that of a point charge at the centre. E=1/4πε₀Q/r²=frac... 1
- In a certain region of space with volume 0.2 m^3, the electric potential is found to be 5 V throughout. The magnitude of electric field in this region is : Answer: 1. zero Electric field is the negative gradient of potential: E=-dV/dx . The potential is constant (5 V) throughout the region, so i... 1
- The increase in the width of the depletion region in a p-n junction diode is due to : Answer: 2. reverse bias only In reverse bias, the applied voltage adds to the barrier. Majority carriers are pulled away from the junction,... 1
- A 40 μF capacitor is connected to a 200 V, 50 Hz ac supply. The rms value of the current in the circuit is, nearly : Answer: 3. 2.5 A Capacitive reactance X_C=1/2π fC . X_C=frac12π×50×40×10⁻⁶≈79.6\ Ω I_rms=fracV_rmsX_C=200/79.6≈2.5\ A Answer: option 3. 1
- The mean free path for a gas, with molecular diameter d and number density n can be expressed as : Answer: 2. 1/√(2) nπ d² The standard result for the mean free path of a gas is λ=1/sqrt2 nπ d² It falls with number density n (more molecule... 1
- For transistor action, which of the following statements is correct ? Answer: 4. The base region must be very thin and lightly doped. For transistor action the base must be very thin and lightly doped, so most... 1
- Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled ? Answer: 4. zero Photoelectric emission needs frequency ν≥ν₀ , whatever the intensity. Initially ν=1.5ν₀ . Halved, it becomes 0.75ν₀<ν₀ , bel... 1
- The calculated spin only magnetic moment of Cr^2+ ion is : Answer: 2. 4.90 BM Spin-only moment: μ=√(n(n+2)) BM, where n is the number of unpaired electrons. Cr (Z=24): 3d⁵4s¹ . mathrmCr²⁺ : 3d⁴ , so... 1
- Which of the following is a basic amino acid ? Answer: 4. Lysine A basic amino acid has an extra basic group (amino) in its side chain. Lysine, H₂N(CH₂)₄CH(NH₂)COOH , has two amino groups... 1
- Which of the following is a natural polymer ? Answer: 1. cis-1,4-polyisoprene Natural rubber is cis-1,4-polyisoprene, a polymer made by plants. Poly(butadiene-styrene) (SBR), polybutadie... 1
- The correct option for free expansion of an ideal gas under adiabatic condition is : Answer: 1. q = 0, Δ T = 0 and w = 0 Free expansion means expansion into vacuum, so external pressure is zero and work w=-P_extΔ V=0 . Adiaba... 1
- The freezing point depression constant (K_f) of benzene is 5.12 K kg mol^-1. The freezing point depression for the solution of molality 0.078 m containing a non-electrolyte solute in benzene is (rounded off upto two decimal places) : Answer: 3. 0.40 K Depression in freezing point: Δ T_f=K_f m . Δ T_f=5.12×0.078=0.399≈0.40\ K Option (3) is correct. 1
- The number of Faradays(F) required to produce 20 g of calcium from molten CaCl_2 (Atomic mass of Ca = 40 g mol^-1) is : Answer: 1. 1 Electrode reaction: mathrmCa²⁺+2e^-→ Ca . One mole of Ca needs 2 F. Moles of Ca =20/40=0.5 mol. Charge =0.5×2=1 F. Answer: opti... 1