NEET UG

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The potential difference (V_A-V_B) between the points A and B in the given figure is Answer: 3. +9 V Move from A to B and add the potential change across each element. Resistor 2 Ω in the direction of current: drop of 2×2=4 V... Kirchhoff's laws and applications 1 answer
A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate d B/dt. Loop 1 of radius R>r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figur… Answer: 3. -dvec B/dtπ r² in loop 1 and zero in loop 2 Induced emf is -dΦ/dt , and flux counts only the area where the field exists. Loop 1... Faraday's law, induced emf and current 1 answer
The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L-C-R circuit. The power factor of this circuit is Answer: 2. 0.8 Power factor cosφ=V_R/V , where V is the supply voltage. V_L-V_C=100-40=60 V. V=√(V_R²+(V_L-V_C)²)=√(80²+60²)=100 V. cosφ=80/... Reactance, impedance, LCR series circuit, resonance 1 answer
Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication? Answer: 2. R=15\ Ω , L=3.5 H, C=30\ μ F Good tuning means a sharp resonance, i.e. a high quality factor Q=1/R√(L/C) . Option √(L/C) ( Ω ) Q... Reactance, impedance, LCR series circuit, resonance 1 answer
A 100 Ω resistance and a capacitor of 100 Ω reactance are connected in series across a 220 V source. When the capacitor is 50% charged, the peak value of the displacement current is Answer: 4. 2.2 A Displacement current in the capacitor gap equals the conduction current in the circuit at every instant, so its peak is the... Reactance, impedance, LCR series circuit, resonance 1 answer
A parallel-plate capacitor of area A, plate separation d and capacitance C is filled with four dielectric materials having dielectric constants k_1,k_2,k_3 and k_4 as shown in the figure below. If a single dielectric material is to be used to have th… Answer: 2. 2/k=3/k₁+k₂+k₃+1/k₄ The upper half (thickness d/2 ) has three dielectrics side by side, each of area A/3 , so they are in paralle... Capacitors, series and parallel combination, parallel plate capacitor with/without dielectric 1 answer
An electric dipole is placed at an angle of 30° with an electric field intensity 2×10^5 N/C. It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2 cm, is Answer: 1. 2 mC Torque on a dipole: τ=pEsinθ , with p=q l . 4=q(0.02)(2×10⁵)sin30^°=q×2000 q=4/2000=2×10⁻³ C =2 mC. Option (1). Electric dipole, field due to dipole, torque in uniform field 1 answer
Starting from the centre of the earth having radius R, the variation of g (acceleration due to gravity) is shown by Answer: 1. graph (1) Inside the earth g is proportional to the distance from the centre; outside it falls as 1/r² . For r For r>R : g=GM/r²... Acceleration due to gravity and its variation with altitude and depth 1 answer
A satellite of mass m is orbiting the earth (of radius R) at a height h from its surface. The total energy of the satellite in terms of g_0, the value of acceleration due to gravity at the earth's surface, is Answer: 1. -mg₀R²/2(R+h) For a satellite in orbit, total energy is half of its (negative) potential energy: E=-GMm/2(R+h) . Use g₀=GM/R² , s... Motion of a satellite: orbital velocity, time period and energy 1 answer
A given sample of an ideal gas occupies a volume V at a pressure P and absolute temperature T. The mass of each molecule of the gas is m. Which of the following gives the density of the gas? Answer: 1. Pm/(kT) Density ρ=mass/volume . Use the ideal gas law in terms of the number of molecules N : PV=NkT . Mass =Nm , so ρ=Nm/V=Pm/kT... Kinetic interpretation of temperature, RMS speed 1 answer
A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be Answer: 1. n²B Field at the centre of a circular coil: B=μ₀ N I/2r . One turn: wire length L=2π r , so B=μ₀ I/2r . n turns from the same wir... Biot-Savart law, field of circular loop 1 answer
An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57×10^-2 T. If the value of e/m is 1.76×10^11 C/kg, the frequency of revolution of the electron is Answer: 4. 1 GHz An electron in a magnetic field circles with frequency f=eB/2π m=1/2π·e/m· B . f=frac1.76×10¹¹×3.57×10⁻²2×3.14=frac6.28×10⁹... Force on moving charge in magnetic and electric fields 1 answer
A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60° is W. Now the torque required to keep the magnet in this new position is Answer: 1. sqrt3W Work to rotate a magnet from equilibrium ( θ=0 ) is W=MB(1-cosθ) ; torque at angle θ is τ=MBsinθ . W=MB(1-cos60^°)=MB/2 ,... Torque on magnetic dipole in uniform field 1 answer
The interference pattern is obtained with two coherent light sources of intensity ratio n. In the interference pattern, the ratio I_max-I_minI_max+I_min will be Answer: 1. 2sqrt n/n+1 With intensities I₁:I₂=n (take I₁=nI₂ ), I_max=(√(I₁)+√(I₂))² and I_min=(√(I₁)-√(I₂))² . fracI_max-I_minI_max+I_min=4... Interference and Young's double-slit experiment 1 answer
Two identical glass (μ_g=3/2) equiconvex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water (μ_w=4/3). The focal length of the combination is Answer: 3. 3f/4 First find the radius of each lens, then the water lens, then combine powers. Glass lens: 1/f=(3/2-1)(2/R)=1/R , so R=f . Wa... Magnification, power of lens, combination of thin lenses 1 answer
A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be Answer: 1. concave, -0.25 diopter The person's far point is 400 cm; to see infinity the lens must form the image of a distant object at 400... Magnification, power of lens, combination of thin lenses 1 answer
An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is Answer: 2. 12 Apparent depth =real depth/μ . The bubble is at a fixed real depth x from one face and t-x from the other. x/1.5=5⇒ x=7.5 cm;... Refraction at plane and spherical surfaces, thin lens and lens maker formula 1 answer
Three sound waves of equal amplitudes have frequencies (n-1), n, (n+1). They superimpose to give beats. The number of beats produced per second will be Answer: 3. 2 Add the three waves of equal amplitude and see how the intensity repeats. y=A[cos2π(n-1)t+cos2π nt+cos2π(n+1)t]=Acos2π nt (1+2c... Beats 1 answer
A body of mass m is attached to the lower end of a spring whose upper end is fixed. The spring has negligible mass. When the mass m is slightly pulled down and released, it oscillates with a time period of 3 s. When the mass m is increased by 1 kg, t… Answer: 3. 9/16 Time period of a spring-mass system is T=2π√(m/k) , so T²∝ m . T₁²/T₂²=m/m+1⇒9/25=m/m+1 9m+9=25m , so 16m=9 and m=9/16 kg. O... Spring oscillations, restoring force, force constant 1 answer
The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length of the open pipe will be Answer: 1. 2L Compare the frequencies using v as the speed of sound. Open pipe of length l : harmonics nv/2l ; the second overtone is the 3r... Standing waves in strings and organ pipes, harmonics 1 answer
A body cools from a temperature 3T to 2T in 10 minutes. The room temperature is T. Assume that Newton's law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be Answer: 1. 3/2T Use Newton's law in the average form: rate of fall =k (mean temperature-T) . First 10 min: 3T-2T/10=k(3T+2T/2-T)=k·3/2T , so... Heat transfer: conduction, convection, radiation 1 answer
Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at 100 °C, while the other one is at 0 °C. If the two bodies are brought into contact, then, assuming no heat loss, the final common t… Answer: 1. more than 50 °C A body with larger heat capacity changes temperature less for the same heat exchanged. The 100 °C body has the la... Specific heat capacity, calorimetry, change of state, latent heat 1 answer
A rectangular film of liquid is extended from (4 cm × 2 cm) to (5 cm × 4 cm). If the work done is 3×10^-4 J, the value of the surface tension of the liquid is Answer: 1. 0.125 N m ⁻¹ Work done in stretching a liquid film is W=T Δ A , where the film has two free surfaces, so Δ A=2×(change in area) .... Surface energy, surface tension, angle of contact, excess pressure, drops, bubbles, capillary rise 1 answer
Three liquids of densities ρ_1,ρ_2 and ρ_3 (with ρ_1>ρ_2>ρ_3), having the same value of surface tension T, rise to the same height in three identical capillaries. The angles of contact θ_1,θ_2 and θ_3 obey Answer: 1. 0≤θ₁<θ₂<θ₃<π/2 Capillary rise is h=2Tcosθ/rρ g . Here h , T and r are the same for all three liquids, so cosθ∝ρ . Since the liqui... Surface energy, surface tension, angle of contact, excess pressure, drops, bubbles, capillary rise 1 answer

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