#neet
- Consider the junction diode as ideal. The value of current flowing through AB is : Answer: 2. 10⁻² A Key idea: check whether the ideal diode is forward or reverse biased. A is at +4 V (on the p-side) and B at -6 V, so the d... 1
- The charge flowing through a resistance R varies with time t as Q = at - bt^2, where a and b are positive constants. The total heat produced in R is : Answer: 1. a³R/6b Key idea: current I=dQ/dt ; heat H=∫ I²R dt . I=a-2bt , which becomes zero at t=a/2b . H=R∫₀^(a/2b)(a-2bt)²dt=R[-(a-2bt)³/... 1
- A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U_1, at wavelength 500 nm is U_2 and that at 1000 nm is U_3. Wien's constant, b = 2.88×10^6 nmK. Which of the following is correct ? Answer: 4. U₂ > U₁ Key idea: Wien's law λ_m T=b gives the wavelength of peak emission. λ_m=dfrac2.88×10⁶5760=500 nm. Emission is maximum at... 1
- Coefficient of linear expansion of brass and steel rods are α_1 and α_2. Lengths of brass and steel rods are l_1 and l_2 respectively. If (l_2 - l_1) is maintained same at all temperatures, which one of the following relations holds good ? Answer: 4. α₁ l₁ = α₂ l₂ Key idea: the difference of lengths stays constant only if both rods expand by the same amount. Δ l₁=Δ l₂⇒ l₁α₁Δ T=... 1
- A npn transistor is connected in common emitter configuration in a given amplifier. A load resistance of 800 Ω is connected in the collector circuit and the voltage drop across it is 0.8 V. If the current amplification factor is 0.96 and the input re… Answer: 1. 4, 3.84 Key idea: in common emitter, A_v=βR_L/R_i and power gain =β A_v . The question uses 0.96 as the current gain β in these f... 1
- The intensity at the maximum in a Young's double slit experiment is I_0. Distance between two slits is d = 5λ, where λ is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at… Answer: 4. I₀/2 Key idea: find the phase difference at the point in front of one slit, then use I=I₀cos²(φ/2) . The point is d/2 from the ce... 1
- A uniform circular disc of radius 50 cm at rest is free to turn about an axis which is perpendicular to its plane and passes through its centre. It is subjected to a torque which produces a constant angular acceleration of 2.0\ rad\ s^-2. Its net acc… Answer: 1. 8.0 Key idea: net acceleration combines tangential and centripetal parts. ω=α t=2×2=4 rad/s. a_t=α r=2×0.5=1 m/s ² ; a_c=ω²r=16×0... 1
- An electron of mass m and a photon have same energy E. The ratio of de-Broglie wavelengths associated with them is : (c being velocity of light) Answer: 1. 1/c(E/2m)^(1/2) Key idea: use λ=h/p for the electron and λ=hc/E for the photon. Electron: p=√(2mE) , so λ_e=h/√(2mE) . Photon: λ_... 1
- A disk and a sphere of same radius but different masses roll off on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first ? Answer: 2. Sphere Key idea: for rolling down an incline, a=gsinθ/1+k²/R² . Smaller k²/R² means larger acceleration and less time. Disk: k²/R... 1
- The angle of incidence for a ray of light at a refracting surface of a prism is 45^°. The angle of prism is 60^°. If the ray suffers minimum deviation through the prism, the angle of minimum deviation and refractive index of the material of the prism… Answer: 2. 30^°;\ √(2) Key idea: at minimum deviation the ray passes symmetrically, so r₁=r₂=A/2 and i=A+δ_m/2 . r=30^° ; μ=sin45^°/sin30^°=... 1
- When an α-particle of mass 'm' moving with velocity 'v' bombards on a heavy nucleus of charge 'Ze', its distance of closest approach from the nucleus depends on m as : Answer: 1. 1/m Key idea: at the closest approach all kinetic energy becomes electrostatic potential energy. 1/2mv²=k(2e)(Ze)/r₀⇒ r₀=4kZe²/mv... 1
- A particle of mass 10 g moves along a circle of radius 6.4 cm with a constant tangential acceleration. What is the magnitude of this acceleration if the kinetic energy of the particle becomes equal to 8×10^-4 J by the end of the second revolution aft… Answer: 1. 0.1\ m/s² Key idea: constant tangential acceleration a gives v²=2as along the arc. 1/2mv²=8×10⁻⁴⇒ v²=dfrac2×8×10⁻⁴0.01=0.16 m ² /... 1
- The molecules of a given mass of a gas have r.m.s. velocity of 200\ ms^-1 at 27^° C and 1.0×10^5\ Nm^-2 pressure. When the temperature and pressure of the gas are respectively, 127^° C and 0.05×10^5\ Nm^-2, the r.m.s. velocity of its molecules in ms^… Answer: 2. 400/√(3) Key idea: v_rms∝sqrt T ; it does not depend on pressure directly for a fixed gas. v₂/v₁=√(400/300)=2/sqrt3 , so v₂=400/s... 1
- A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross - section. The ratio of the magnetic fields B and B', at radial distances a/2 and 2a respectively, from the axis of the wire is : Answer: 3. 1 Key idea: use Ampere's law. Inside the wire, B=μ₀Ir/2π a² ; outside, B=μ₀I/2π r . At r=a/2 : B=μ₀I/4π a . At r=2a : B'=μ₀I/4π a... 1
- A particle moves so that its position vector is given by r = ω t x + ω t y. Where ω is a constant. Which of the following is true ? Answer: 3. Velocity is perpendicular to r and acceleration is directed towards the origin. Key idea: this is uniform circular motion of unit... 1
- What is the minimum velocity with which a body of mass m must enter a vertical loop of radius R so that it can complete the loop ? Answer: 4. √(5gR) Key idea: at the top the minimum speed satisfies mg=mv_t²/R , so v_t²=gR . Energy conservation from bottom to top (height... 1
- A n-p-n transistor is connected in common emitter configuration (see figure) in which collector voltage drop Ans: (4) 1 mA Sol. Voltage drop across load resistance, VL = ICRC 0.8 = IC × 800 IC = 1 mA 1
- If E and G respectively denote energy and gravitational constant, then E /G has the dimensions of: Correct answer: (2) [M²] [L⁻¹] [T⁰] Explanation: E = energy = [ML²T⁻²] G = Gravitational constant = [M⁻¹L³T⁻²] So E/G = [E]/[G] = ML²T⁻²over... 1
- How to Score 170 Plus in NEET Physics 2022 ?| नीट फिजिक्स 2022 में 170 प्लस कैसे स्कोर करें? परीक्षा नजदीक होने के साथ, छात्र अपना अधिकांश समय बनाने में कोई कसर नहीं छोड़ रहे हैं और उस पूर्ण स्कोर को प्राप्त करने के लिए अपना सर्वश्रे... 1