neet physics tutor doubt 6: 45 Premium NEET Physics Questions Selected by Kumar Sir

Question 1. A particle moves such that its acceleration is given by a = - p(x - c), where p and c are positive constants. Time period of oscillations of particles is

1. 2π√c
2. 2π 1√(p + c)
3. 2π√p
4. 2π 1√(p - c)

Question 2. The ratio of lengths, radii and Young moduli of two wires of material A and B are x, y and z respectively. The ratio of increase in their lengths is

1. 3x2y²z
2. xy²2z
3. 2xy²3
4. 2x3y²z

Question 3. A wall is made of two layers P and Q of same thickness but different materials. The thermal conductivity of P is thrice that of Q. In steady state, temperature difference across the wall is 36°C. The temperature difference across layer P is

1. 10°C
2. 12°C
3. 9°C
4. 15°C

Question 4. A gas mixture consists of 2 moles of oxygen and 4 moles of helium at absolute temperature T. Neglecting all vibrational modes, the total internal energy of system is

1. 11 RT
2. 14 RT
3. 9 RT
4. 15 RT

Question 5. Two persons A and B standing at ends of a plank of length 5 m and mass 80 kg swap their positions. The plank is placed on a smooth horizontal surface and masses of A and B are 60 kg and 40 kg respectively. What is displacement of A with respect to the horizontal surface?

1. 609 m
2. 409 m
3. 507 m
4. 556 m

Question 6. A particle of mass 4 kg is thrown from ground with speed of 50 m/s at an angle of 53° from horizontal. Torque on it about point of projection at time t (t < time of flight) is

1. (1200 t) Nm
2. (550 t) Nm
3. (600 t) Nm
4. (880 t) Nm

Question 7. P-V diagram for an ideal gas is shown in process. At A and B, internal energy of gas is 10 J and 50 J respectively. If heat given to gas during the process BC is 60 J, then internal energy of gas in the state C is

1. 180 J
2. 200 J
3. 250 J
4. 150 J

Question 8. Current I in an inductor coil varies with time t, according to the adjoining graph. The graph which correctly shows the variation of voltage in the coil is

1. Graph (1)
2. Graph (2)
3. Graph (3)
4. Graph (4)

Question 9. A square metal loop of side 10 cm and resistance 1 Ω is moved with constant velocity partly inside a uniform magnetic field 2 T, directed into the paper as shown. The loop is connected to a network of three resistors R = 3 Ω. If steady current of 2 mA flows in loop, then speed of loop is

1. 1 cm/s
2. 2 cm/s
3. 0.5 cm/s
4. 4 cm/s

Question 10. The work functions for two metals P and Q are φ₁ and φ₂ respectively with φ₁ > φ₂. The graphs between stopping potential (V₀) and frequency (ν) of incident radiation for them would look like

1. Graph (1)
2. Graph (2)
3. Graph (3)
4. Graph (4)

Question 11. An electron with kinetic energy K (eV) collides with hydrogen atom in ground state. The collision is observed to be elastic for

1. 0 < K < ∞
2. Only 0 < K < 3.4 eV
3. 0 < K < 10.2 eV
4. 0 < K < 13.6 eV

Question 12. The fraction of the initial activity of a radioactive material which remains after half of a half-life of the radioactive sample is

1. 0.707
2. 0.37
3. 0.63
4. 0.5

Question 13. Electric field in a region is given by E = (2x î + 4y ĵ) V/m where x and y are in metre. A charged particle 1 C is moved from origin to point P(2 m, 4 m), first along the y-axis and then along x-axis. The work done by field is

1. Zero
2. 36 J
3. 26 J
4. 20 J

Question 14. The electric potential V in space as a function of co-ordinates is given by V = 1/x + 1/y + 1/z. The electric field intensity at (2, 2, 2) is given by (in V/m)

1. î + ĵ + k̂
2. î + ĵ + k̂2
3. 2î + 2ĵ + 2k̂
4. î + ĵ + k̂4

Question 15. For a satellite to appear stationary to an observer on earth, which of the following is false?

1. Its sense of rotation must be from west to east
2. It must be rotating about the Earth's axis
3. It must be rotating in the equatorial plane
4. Its time period must be 84.6 min

Question 16. A uniform wire of resistance 8 Ω is bent into the form of circle of radius r. A specimen of same wire is connected along the diameter of the circle. The equivalent resistance across the ends of this wire is

1. (48 + π) Ω
2. (84 + 3π) Ω
3. (84 + π) Ω
4. (84 + 2π) Ω

Question 17. An electric heater is designed to operate in 200 V mains with output of 1000 W. When it is connected to 50 V source, power output is

1. 62.5 W
2. 250 W
3. 500 W
4. 1000 W

Question 18. A capacitor of capacity C₁ = 10 μF is charged to 40 V and a second capacitor of capacity C₂ = 15 μF is charged to 30 V. If they are connected in parallel, with like charged plates, the charge flow is

1. 20 μC
2. 45 μC
3. 60 μC
4. 75 μC

Question 19. A positive charged particle q, mass m is dropped from certain point above ground. A constant horizontal magnetic field of magnitude B is present. If charge falls down by height h, then speed of charge is (neglect effect of air)

1. √(2gh)
2. √(2gh + qB/m)
3. √(qB/m)
4. √(gh + qB/2m)

Question 20. If ratio of time periods of circular motion of two charged particles in magnetic field is 1 : 2, and they have same charge and same speed, then the ratio of their kinetic energies is

1. 1 : 1
2. 1 : 2
3. 2 : 1
4. 1 : √2

Question 21. If a magnetic dipole of dipole moment M is rotated through an angle θ with respect to the direction of magnetic field B, then work done by field is

1. -MB cosθ
2. MB[1 - cosθ]
3. MB[sinθ - 1]
4. MB[cosθ - 1]

Question 22. A plane mirror of length L moves vertically along y-axis as shown in figure with velocity v. A point source S illuminates mirror. The rate at which length of light spot is growing on wall is

1. Zero
2. v
3. 2v
4. 4v

Question 23. A ray of light is incident at angle 60° on a prism kept in air. The angle of refraction of prism, angle of deviation and angle of emergence are equal. The refractive index of prism is

1. 1.414
2. 1.73
3. 1.67
4. 1.33

Question 24. Two incoherent waves of intensities I₀ and 4I₀ superimpose at a place. What is resultant intensity at that point?

1. 4I₀
2. 5I₀
3. 7I₀
4. 3I₀

Question 25. In YDSE experiment, electron beam is used in place of light which was accelerated through some potential difference. If accelerating potential difference is made four times, then width of fringes will become

1. 2 times
2. 4 times
3. 12 times
4. 14 times

Question 26. A particle moves along x-axis in such a way that distance covered by it in any second exceeds that in the previous second by 2 m. If it covers 1 m distance in the first second, then its distance at the end of n seconds is (in metre)

1. 2n
2. n²
3. n³
4. 2n²

Question 27. A boatman finds that he can save 2 seconds in crossing a river by the quickest path, than by the shortest path. If velocity of boat in still water is 13 m/s and speed of flow of water is 5 m/s, then width of river is

1. 189 m
2. 408 m
3. 256 m
4. 312 m

Question 28. A very small block of weight W is pulled at uniform velocity by a constant force F, through a string AB having length a. The end B is at height b above the horizontal rough surface. The coefficient of friction between block and horizontal surface is

1. W(a + b)F(a - b)
2. F√(a² - b²)Wa - Fb
3. W√(a² + b²)F(b - a)
4. F(a - b)W√(a² + b²)

Question 29. The magnitude of the force acting along (6î - 2k̂ + 3ĵ), which displaces a particle from (2, 1, 0) to (1, 4, -1) and does work 5 J, is

1. 11 N
2. 7 N
3. 15 N
4. 9 N

Question 30. Efficiency of a water pump is 80% and it lifts 25 kg water per second to 8 m height. The power consumed by pump is

1. 2.5 kW
2. 2.0 kW
3. 1.6 kW
4. 2.4 kW

Question 31. Four particles each having mass m are placed at the four corners of a square having edge length l. The moment of inertia of system about an axis along its one diagonal is

1. 4 ml²
2. 2ml²
3. ml²
4. ml²2

Question 32. Select incorrect statement.

1. For mountains, the position of centre of gravity will be below that of centre of mass of mountain.
2. Centre of mass of regular bodies is always at its geometrical centre.
3. The centre of mass is closer to the heavier mass compared to a lighter mass.
4. Centre of mass may lie outside an object.

Question 33. Within proportional limit, the slope of the stress-strain curve yields

1. Elastic fatigue
2. Modulus of elasticity
3. Poisson's ratio
4. Working stress

Question 34. The terminal speed of a spherical rain drop of mass m and radius r, falling through air is proportional to

1. mr²
2. mr
3. r²
4. mr³

Question 35. If velocity of light (3 × 10⁸ m/s), acceleration due to gravity (9.8 m/s²) and density of water (10³ kg/m³) are adopted as the fundamental units, then unit of length will be

1. 6.2 × 10¹⁶ m
2. 4 × 10¹⁷ m
3. 10.5 × 10¹² m
4. 9.2 × 10¹⁵ m

Question 36. A particle executes SHM between two points separated by 20 cm along x-axis. If the force experienced by it be 2 N at displacement 1 cm from mean position, then the maximum force experienced by it is

1. 20 N
2. 40 N
3. 10 N
4. 80 N

Question 37. If the difference in frequencies corresponding to tones emitted by stretched string vibrating in its 2nd overtone and seventh harmonic is 1600 Hz, then fundamental frequency of string is

1. 200 Hz
2. 400 Hz
3. 800 Hz
4. 600 Hz

Question 38. The emission spectrum of a black body at two different temperatures are as shown by curves x and y. The ratio of the area under the two curves x and y is

1. 1 : 2
2. 2 : 1
3. 1 : 16
4. 16 : 1

Question 39. A diode of Si is used in a circuit as shown in figure. The electric current through cell is

1. Zero
2. 10^-4 A
3. 10^-3 A
4. 10^-2 A

Question 40. The Boolean equation for circuit shown in figure is

1. A.B
2. A + B
3. A.B
4. A.B

Question 41. A transistor operating in common emitter configuration and change in base current from 200 μA to 250 μA produces change in collector current from 10 mA to 15 mA. The current gain is

1. 150
2. 90
3. 50
4. 100

Question 42. The intensity of electromagnetic wave is equal to (symbols have their usual meanings)

1. ε₀E_rmsB_rmsc²
2. ε₀E_rms²
3. ε₀E_rmsB_rms
4. ε₀B_rms²c

Question 43. At resonance in a series LCR circuit, if the input voltage is V_in and the quality factor is Q, then the voltage across the inductor is

1. V_in/Q
2. V_in
3. QV_in
4. Q²V_in

Question 44. According to Weiss theory, ferromagnetism arises due to

1. interaction of spin of electrons of one atom with that of neighbouring atoms
2. interaction of orbital motion of electrons with the nucleus
3. random thermal motion of magnetic domains
4. motion of free electrons through the crystal lattice

Question 45. A particle of mass M moving with velocity u collides elastically in one dimension with a stationary particle of mass 2M. The impulse on the first particle is

1. -Mu/3
2. -2Mu/3
3. -Mu
4. -4Mu/3