#neet
- pH of a saturated solution of Ca(OH)_2 is 9. The solubility product (K_sp) of Ca(OH)_2 is : Answer: 1. 0.5×10⁻¹⁵ Use pH to get [OH^-] , then write K_sp . pH = 9 so pOH = 5 and [OH^-] = 10⁻⁵ M. mathrmCa(OH)₂ ⇌ Ca²⁺ + 2OH^- , so [math... 1
- If the rate constant for a first order reaction is k, the time (t) required for the completion of 99% of the reaction is given by : Answer: 3. t = 4.606/k For a first order reaction t = 2.303/klog[A]₀/[A] . When 99% is complete, [A] = 0.01[A]₀ , so t = 2.303/klog 100 = 2.... 1
- The unit of thermal conductivity is : Answer: 4. W m ⁻¹ K ⁻¹ From Q/T=KA Δθ/L , K=(Q/t) L/A Δθ . Unit of Q/t is W, L is m, A is m ² , Δθ is K. So K has unit W m/m² K=W m⁻¹K⁻¹ . 1
- Which of the following acts as a circuit protection device ? Answer: 4. fuse A fuse contains a thin wire that melts when the current exceeds a safe limit, breaking the circuit and protecting the applia... 1
- α-particle consists of : Answer: 1. 2 protons and 2 neutrons only An α -particle is the nucleus of a helium atom, ⁴₂He : 2 protons and 2 neutrons, with no electrons. 1
- The displacement of a particle executing simple harmonic motion is given byy = A_0 + Aω t + Bω t.Then the amplitude of its oscillation is given by : Answer: 2. √(A²+B²) The constant A₀ only shifts the mean position. The oscillating part is Asinω t+Bcosω t . Write it as Csin(ω t+φ) with Cc... 1
- Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is F_1. When the space between the two lenses is filled with glycerin (which has the same refract… Answer: 2. 1 : 2 Two thin lenses in contact: dfrac1F₁=1/f+1/f , so F₁=f/2 . When the gap is filled with glycerin of the same index as glass,... 1
- Increase in temperature of a gas filled in a container would lead to : Answer: 2. increase in its kinetic energy The temperature of a gas measures the average kinetic energy of its molecules. Raising the tempera... 1
- An electron is accelerated through a potential difference of 10,000 V. Its de Broglie wavelength is, (nearly) : (m_e = 9×10^-31 kg) Answer: 2. 12.2×10⁻¹² m de Broglie wavelength of an electron accelerated through V : λ=h/√(2meV) . Substituting h=6.63×10⁻³⁴ , m=9×10⁻³¹ , e... 1
- A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is : (α_Cu = 1.7×10^-5 K^-1 and α_Al = 2.2×10^-5 K^-1) Answer: 4. 68 cm The difference in length stays the same at all temperatures only if both rods expand by the same amount: Δ l_Cu=Δ l_Al . l_... 1
- Pick the wrong answer in the context with rainbow. Answer: 3. An observer can see a rainbow when his front is towards the sun. We pick the wrong statement. Two internal reflections give the s... 1
- A body weighs 200 N on the surface of the earth. How much will it weigh half way down to the centre of the earth ? Answer: 4. 100 N Inside the earth at depth d , g'=g(1-d/R) . Halfway to the centre means d=R/2 , so g'=g/2 . Weight =200/2=100 N. 1
- Six similar bulbs are connected as shown in the figure with a DC source of emf E, and zero internal resistance.The ratio of power consumption by the bulbs when (i) all are glowing and (ii) in the situation when two from section A and one from section… Answer: 2. 9 : 4 From the figure, the three bulbs of section A are in parallel with each other, as are the three bulbs of section B. The two... 1
- For a p-type semiconductor, which of the following statements is true ? Answer: 2. Holes are the majority carriers and trivalent atoms are the dopants. A p-type semiconductor is made by doping silicon or germaniu... 1
- Average velocity of a particle executing SHM in one complete vibration is : Answer: 4. zero Average velocity =displacement/time . In one complete vibration the particle returns to its starting point, so the displacem... 1
- A solid cylinder of mass 2 kg and radius 4 cm is rotating about its axis at the rate of 3 rpm. The torque required to stop after 2π revolutions is : Answer: 1. 2×10⁻⁶ N m Find the angular deceleration from the rotation kinematics, then use τ=Iα . ω₀=3 rpm =3×2π/60=0.1π rad/s. Angle turned... 1
- A force F = 20 + 10y acts on a particle in y-direction where F is in newton and y in meter. Work done by this force to move the particle from y = 0 to y = 1 m is : Answer: 3. 25 J Work done by a variable force is W=∫ F dy . W=∫₀¹(20+10y) dy=[20y+5y²]₀¹=20+5=25 J. 1
- In the circuits shown below, the readings of the voltmeters and the ammeters will be : Answer: 3. V₁ = V₂ and i₁ = i₂ Treat the voltmeters as ideal (infinite resistance), so they draw no current. Circuit 1: the 10 Ω resistor is... 1
- A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the centre : Answer: 2. zero as r increases for r < R, decreases as r increases for r > R For a uniformly charged hollow sphere, by Gauss's law: Inside (... 1
- At a point A on the earth's surface the angle of dip, δ = +25^°. At a point B on the earth's surface the angle of dip, δ = -25^°. We can interpret that : Answer: 3. A is located in the northern hemisphere and B is located in the southern hemisphere. The angle of dip is positive (the north pole... 1
- The total energy of an electron in an atom in an orbit is -3.4 eV. Its kinetic and potential energies are, respectively : Answer: 3. 3.4 eV, -6.8 eV For an electron in a bound orbit, KE=-E and PE=2E . With E=-3.4 eV: KE=+3.4 eV and PE=-6.8 eV. Check: 3.4-6.8=-3.... 1
- In total internal reflection when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction ? Answer: 4. 90^° At the critical angle C , Snell's law gives μ₁sin C=μ₂sin r with sin C=μ₂/μ₁ . So sin r=1 and r=90^° : the refracted ray gra... 1
- The work done to raise a mass m from the surface of the earth to a height h, which is equal to the radius of the earth, is : Answer: 3. 1/2mgR Work done = change in gravitational potential energy. W=-GMm/R+h+GMm/R . With h=R : W=GMm(1/R-dfrac12R)=GMm/2R . Using GM=... 1
- When an object is shot from the bottom of a long smooth inclined plane kept at an angle 60^° with horizontal, it can travel a distance x_1 along the plane. But when the inclination is decreased to 30^° and the same object is shot with the same veloci… Answer: 3. 1:√(3) On a smooth incline the retardation is gsinθ . For the same launch speed v , the distance up the plane is x=v²/2gsinθ , so... 1