NEET UG

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The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance Answer: 4. 13.89 H Energy stored in an inductor: U=1/2LI² . L=2U/I²=frac2×25×10⁻³(60×10⁻³)²=frac0.053.6×10⁻³≈13.89\ H Self and mutual inductance 1 answer
An em wave is propagating in a medium with a velocity V=V i. The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along Answer: 3. + z direction In an em wave, vec E , vec B and the direction of propagation are mutually perpendicular, and vec E×vec B points al... EM waves, characteristics and transverse nature 1 answer
In the combination of the following gates the output Y can be written in terms of inputs A and B as Answer: 3. A·B+A· B Read the figure: the upper AND gate gets A and overline B ; the lower AND gate gets overline A and B . An OR gate joins... Logic gates (OR, AND, NOT, NAND, NOR) 1 answer
In a p-n junction diode, change in temperature due to heating Answer: 4. affects the overall V - I characteristics of p-n junction Heating changes the number of thermally generated electron-hole pairs,... p-n junction diode I-V characteristics 1 answer
The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is Answer: 1. independent of the distance between the plates. The field of one plate is σ/2ε₀ , and this acts on the charge Q of the other plat... Capacitors, series and parallel combination, parallel plate capacitor with/without dielectric 1 answer
In the circuit shown in the figure, the input voltage V_i is 20 V, V_BE = 0 and V_CE = 0. The values of I_B, I_C and β are given by Answer: 4. I_B = 40 μ A, I_C = 5 mA, β = 125 From the figure: R_B=500\ kΩ , R_C=4\ kΩ , supply 20 V, V_i=20 V, with V_BE=0 and V_CE=0 . I_B=... Semiconductors 1 answer
An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it throu… Answer: 1. smaller The force magnitude is eE for both particles, so a=eE/m . Fall distance h=1/2at² gives t=√(2h/a) . The electron has a muc... Electric field, field lines, field of point charge 1 answer
A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 27°C two successive resonances are produced at 20 cm and 73 cm of column length. If the… Answer: 3. 339 m/s In a resonance tube, two successive resonances are half a wavelength apart. dfracλ2=73-20=53 cm, so λ=106 cm =1.06 m. v=f... Speed of sound by resonance tube 1 answer
A student measured the diameter of a small steel ball using a screw gauge of least count 0.001 cm. The main scale reading is 5 mm and zero of circular scale division coincides with 25 divisions above the reference level. If screw gauge has a zero err… Answer: 4. 0.529 cm Observed reading =0.5+25×0.001=0.525 cm. Zero error is -0.004 cm, so the correction is +0.004 cm. d=0.525-(-0.004)=0.529... Vernier calipers and screw gauge 1 answer
In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20^°. To increase… Answer: 3. 1.9 mm Angular fringe width is θ=λ/d , so θ∝1/d for fixed λ . d₂/d₁=θ₁/θ₂⇒ d₂=2×0.20/0.21≈1.9\ mm The slit separation must be dec... Interference and Young's double-slit experiment 1 answer
An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of Answer: 2. large focal length and large diameter Angular magnification of an astronomical telescope is m=f_o/f_e , so a large objective foca... Microscope and astronomical telescope 1 answer
Unpolarised light is incident from air on a plane surface of a material of refractive index 'μ'. At a particular angle of incidence 'i', it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options… Answer: 3. Reflected light is polarised with its electric vector perpendicular to the plane of incidence When reflected and refracted rays a... Polarization, Brewster's law, Polaroids 1 answer
An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be Answer: 3. 36 cm away from the mirror Use the mirror formula 1/v+1/u=1/f with f=-15 cm. Case 1: u=-40 : 1/v=-dfrac115+dfrac140=-5/120⇒ v=-24... Reflection, spherical mirrors, mirror formula 1 answer
The refractive index of the material of a prism is 2 and the angle of the prism is 30^°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face… Answer: 3. 45^° The ray retraces its path only if it strikes the silvered face normally. The prism angle is A=30^° . For a ray hitting the s... Refraction through a prism 1 answer
A pendulum is hung from the roof of a sufficiently high building and is moving freely to and fro like a simple harmonic oscillator. The acceleration of the bob of the pendulum is 20 m/s^2 at a distance of 5 m from the mean position. The time period o… Answer: 3. π s For SHM, a=ω²x . ω²=20/5=4⇒ω=2\ mathrmrad s⁻¹ . T=2π/ω=π\ s Simple pendulum 1 answer
Two wires are made of the same material and have the same volume. The first wire has cross-sectional area A and the second wire has cross-sectional area 3A. If the length of the first wire is increased by Δ l on applying a force F, how much force is… Answer: 1. 9 F Same volume: A l=3A l₂ , so the second wire has length l₂=l/3 . From Y=F l/A Δ l , F=YAΔ l/l . F₂=Y(3A)Δ l/l/3=9·YAΔ l/l=9F Elastic behaviour, stress-strain, Hooke's law, Young's, bulk and rigidity moduli 1 answer
The power radiated by a black body is P and it radiates maximum energy at wavelength, λ_0. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 34λ_0, the power radiated by it becomes nP. The value of n… Answer: 2. 256/81 Wien's law: λ_mT= constant, so T∝dfrac1λ_m . Stefan's law: P∝ T⁴ . New wavelength is 3/4λ₀ , so T'=4/3T . n=(4/3)⁴=256/81 Heat transfer: conduction, convection, radiation 1 answer
A small sphere of radius 'r' falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to Answer: 2. r⁵ At terminal velocity, heat is produced at the rate equal to the power of the viscous force: P=F v_t=6πη r v_t² . Terminal velo... Viscosity, Stokes' law, terminal velocity, streamline and turbulent flow, critical velocity 1 answer
The moment of the force, F=4 i+5 j-6 k at (2, 0, -3), about the point (2, -2, -2), is given by Answer: 4. -7hat i-4hat j-8hat k Moment (torque) about a point: vecτ=vec r×vec F , where vec r goes from the point to the point of applicati... Moment of force, torque 1 answer
A sample of 0.1 g of water at 100°C and normal pressure (1.013×10^5 Nm^-2) requires 54 cal of heat energy to convert to steam at 100°C. If the volume of the steam produced is 167.1 cc, the change in internal energy of the sample, is Answer: 3. 208.7 J First law: Δ U=Q-W , with W=PΔ V . Q=54×4.18≈225.7 J. Volume change: steam 167.1 cc minus water 0.1 cc, Δ V=167\ cm³=1.67... First law of thermodynamics 1 answer
An inductor 20 mH, a capacitor 100 μF and a resistor 50 Ω are connected in series across a source of emf, V = 10 sin 314 t. The power loss in the circuit is Answer: 1. 0.79 W Power is lost only in the resistor: P=I_rms²R , with I_rms=V_rms/Z . X_L=ω L=314×0.02=6.28\ Ω ; X_C=1/ω C=dfrac1314×10⁻⁴=3... Power in AC circuits, wattless current 1 answer
A long solenoid of diameter 0.1 m has 2×10^4 turns per meter. At the centre of the solenoid, a coil of 100 turns and radius 0.01 m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to 0A… Answer: 2. 32 μ C Key idea: charge q=ΔΦ/R (independent of the time taken). Field inside solenoid B=μ₀nI . Change: Δ B=4π×10⁻⁷×2×10⁴×4=0.032π... Self and mutual inductance 1 answer
The x and y coordinates of the particle at any time are x = 5t - 2t^2 and y = 10t respectively, where x and y are in meters and t in seconds. The acceleration of the particle at t = 2s is : Answer: 2. - 4 m/s ² Key idea: acceleration components are second derivatives of position. a_x=d²x/dt²=-4 m/s ² , a_y=d²y/dt²=0 . Accelerati... Frame of reference, motion in a straight line, speed and velocity 1 answer
At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth's atmosphere ?(Given :Mass of oxygen molecule (m) = 2.76×10^-26 kgBoltzmann's constant k_B = 1.38×10^-23 J K^-1) Answer: 3. 8.360×10⁴ K The molecules escape only if their rms speed equals the escape speed of the Earth, v_e = 11.2\ mathrmkm s⁻¹ = 1.12×10... Kinetic interpretation of temperature, RMS speed 1 answer

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