Magnetism & Matter PYQs Set 2 (PDF)

Set 2 of 6 · Questions 31-60 of 176

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Mere Teacher · Previous Year Questions JEE Main Physics · Magnetism & Matter · Set 2 (Q31-60)
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31. $A boy’s catapult is made of rubber made of a rubber cord of length 42 cm long, with 6 mm diameter of cross-section and of negligible mass. The boy keeps a stone weighing 0.02 kg on it and stretches the cord by 20 cm by applying a constant force. When released, the stone flies off with a velocity of 20 ms^{- 1} . Neglect the change in the area of cross-section of the cord while stretched. The Young’s modulus of rubber is closest to:$ (1) $10^{6} N / m^{- 2}$ (2) $10^{4} N / m^{- 2}$ (3) $10^{8} N / m^{- 2}$ (4) $10^{3} N / m^{- 2}$ 32. $The net magnetic flux through any closed surface is [NEET 2023]$ (1) $positive$ (2) $infinity$ (3) $negative$ (4) $zero$ 33. $The magnetic field lines of a bar magnet$ (1) $leave from the south pole of the ma$ (2) $are absent inside the magnet$ (3) $intersect each other$ (4) $form continuous closed loops$ 34. $A bar magnet is released from rest along the axis of a very long vertical copper tube. After some time the magnet will$ (1) $Move down with an acceleration equal to g$ (2) $Oscillate inside the tube$ (3) $Move down with almost constant speed$ (4) $Move down with an acceleration greater than g$ 35. $A magnetic dipole experiences a torque of 803 N m when placed in uniform magnetic field in such a way that dipole moment makes angle of 60^{\circ} with magnetic field. The potential energy of the dipole is:$ (1) $- 403 J$ (2) $-80 J$ (3) $80 J$ (4) $-60 J$ 36. $Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion (A): Electromagnets are made of soft iron. Reason (R): Soft iron has high permeability and low retentivity. In the light of above statements, choose the most appropriate answer from the options given below.$ (1) $A is not correct but R is correct$ (2) $A is correct but R is not correct$ (3) $Both A and R are correct and R is the correct explanation of A$ (4) $Both A and R are correct but R is not the correct explanation of A$ 37. $The magnetic susceptibility of a paramagnetic material at - 73^{\circ} C is 0.0075 and its value at - 173^{\circ} C will be$ (1) $0.0030$ (2) $0.0075$ (3) $0.0045$ (4) $0.015$ 38. $A uniform conducting wire of length 12a and resistance R is wound up as a current (I) carrying coil in the shape of (A) an equilateral triangle of side a. (B) a square of side a. The magnetic dipole moments of the coil in each case respectively are [NEET 2021]$ (1) $3 I a^{2} and 3 I a^{2}$ (2) $3 I a^{2} and I a^{2}$ (3) $3 I a^{2} and 4 I a^{2}$ (4) $4 I a^{2} and 3 I a^{2}$ 39. $A short bar magnet of magnetic moment 0.4 J T^{1} is placed in a uniform magnetic field of 0.16 T . The magnet is in stable equilibrium when the potential energy is$ (1) $0.0647 J$ (2) $- 0.064 J$ (3) $zero$ (4) $- 0.082 J$ 40. $At a location, the horizontal components of the earth's magnetic field is 0.3 G in the magnetic meridian and the dip angle is 60^{\circ} . The earth's magnetic field at this location in G is$ (1) $0.3$ (2) $0.6$ (3) $0.9$ (4) $1.2$ 41. $A rectangular coil of length 0.12 m and width 0.1 m having 50 turns of wire is suspended vertically in a uniform magnetic field of strength 0.2 Weber / m^{2} . The coil carries a current of 2 A. If the plane of the coil is inclined at an angle of 3 0^{o} with the direction of the field, the torque required to keep the coil in stable equilibrium will be$ (1) $0.24 Nm$ (2) $0.12 Nm$ (3) $0.15 Nm$ (4) $0.20 Nm$ 42. $At a point A on the earth’s surface the angle of dip, δ = + 2 5^{o} . At a point B on the earth’s surface the angle of dip, δ = - 2 5^{o} . We can interpret that$ (1) $A and B are both located in the southern hemisphere.$ (2) $A and B are both located in the northern hemisphere.$ (3) $A is located in the southern hemisphere and B is located in the northern hemisphere.$ (4) $A is located in the northern hemisphere and B is located in the southern hemisphere.$ 43. $If ‘M’ is the mass of water that rises in a capillary tube of radius 'r', then mass of water which will rise in a capillary tube of radius '2r' is:$ (1) $M$ (2) $\frac{M}{2}$ (3) $4 M$ (4) $2 M$ 44. $The magnetic field (B) inside a long solenoid having n turns per unit length and carrying current I when iron core is kept in it is (μ_{0} = permeability of vacuum, χ = magnetic susceptibility)$ (1) $μ_{0} nI (1 - χ)$ (2) $μ_{0} nI χ$ (3) $μ_{0} n I^{2} (1 + χ)$ (4) $μ_{0} nI (1 + χ)$ 45. $A paramagnetic material has 10^{28} atoms / m^{3} . Its magnetic susceptibility at temperature 350 K is 2.8 \times 10^{- 4} . Its suscetibility at 300 K is:$ (1) $3.267 \times 10^{- 4}$ (2) $3.672 \times 10^{- 4}$ (3) $3.726 \times 10^{- 4}$ (4) $2.672 \times 10^{- 4}$ 46. $Ferromagnetic materials used in a transformer must have$ (1) $low permeability and high hysterisis loss$ (2) $high permeability and low hysterisis loss$ (3) $high permeability and high hysterisis loss$ (4) $low permeability and low hysterisis loss.$ 47. $If M_{z} = magnetization of a paramagnetic sample, B = external magnetic field, T = absolute temperature, C = curie constant. Then according to Curie's law in magnetism, the correct relation is$ (1) $M_{z} = \frac{T}{CB}$ (2) $M_{z} = \frac{CB}{T}$ (3) $C = \frac{M _{z} B}{T}$ (4) $C = \frac{T ^{2}}{M _{z} B}$ 48. $Which of the following statement proves that earth has magnetic field?$ (1) $Earth is surrounded by ionosphere.$ (2) $The intensity of cosmic rays stream of charged particles is more as the poles then at the equator.$ (3) $A large quantity of iron-ore is found in the earth.$ (4) $Earth is a planet rotating about the North South axis.$ 49. $At 40° C, a brass wire of 1 mm radius is hung from the ceiling. A small mass, M is hung from the free end of the wire. When the wire is cooled down from 40ºC to 20ºC it regains its original length of 0.2 m. The value of M is close to: (Coefficient of linear expansion and Young’s modulus of brass are 10^{- 5} /° C and 10^{11} N / m^{2}, respectively; g = 10 ms^{- 2})$ (1) $9 kg$ (2) $0.5 kg$ (3) $1.5 kg$ (4) $6.28 kg$ 50. $χ_{1} and χ_{2} are susceptibility of a paramagnetic material at temperatures T_{1} K and T_{2} K respectively, then$ (1) $χ_{1} = χ_{2}$ (2) $χ_{1} T_{1} = χ_{2} T_{2}$ (3) $χ_{1} T_{2} = χ_{2} T_{1}$ (4) $χ_{1} T_{1} = χ_{2} T_{2}$ 51. $A charge q is spread uniformly over an isolated ring of radius R . The ring is rotated about its natural axis with an angular velocity ω . Magnetic dipole moment of the ring is$ (1) $\frac{qω R ^{2}}{2}$ (2) $\frac{qωR}{2}$ (3) $qω R^{2}$ (4) $\frac{qω}{2 R}$ 52. $The magnetic susceptibility of ferromagnetic materials is$ (1) $< 0$ (2) $> 1$ (3) $1$ (4) $0$ 53. $Electromagnets are made of soft iron because soft iron has$ (1) $low retentivity and high coercive force$ (2) $high retentivity and high coercive force$ (3) $low retentivity and low coercive force$ (4) $high retentivity and low coercive force$ 54. $A vibration magnetometer is used at two different places A and B on the earth. The time period of a magnet suspended freely in the magnetometer at A is twice that at B . If the horizontal component of the earth's magnetic field at B is 32 \times 10^{- 6} T, then its value at A is$ (1) $H_{A} = 8 \times 10^{- 6} T$ (2) $H_{A} = 32 \times 10^{- 6} T$ (3) $H_{A} = 4 \times 10^{- 6} T$ (4) $H_{A} = 16 \times 10^{- 6} T$ 55. $Let m and r are the dipole moment and radius of earth respectively. Then, the earth's magnetic field at the equator is$ (1) $\frac{μ _{0} m}{4 π r ^{3}}$ (2) $\frac{μ _{0} m}{8 π r ^{3}}$ (3) $\frac{μ _{0} m}{2 π r ^{3}}$ (4) $\frac{μ _{0} m}{π r ^{3}}$ 56. $The elastic limit of brass is 379 MPa. What should be the minimum diameter of a brass rod if it is to support a 400 N load without exceeding its elastic limit?$ (1) $1.00 mm$ (2) $1.16 mm$ (3) $0.90 mm$ (4) $1.36 mm.$ 57. $Materials suitable for permanent magnets, must have which of the following properties?$ (1) $High retentivity, low coercivity and high permeability.$ (2) $Low retentivity, low coercivity and low permeability.$ (3) $Low retentivity, high coercivity and low permeability.$ (4) $High retentivity, high coercivity and high permeability.$ 58. $The soft-iron is a suitable material for making an electromagnet. This is because soft-iron has:$ (1) $low coercively and high retentively$ (2) $low coercively and low permeability$ (3) $high permeability and low retentively$ (4) $high permeability and high retentively$ 59. $A material of 0.25 cm^{2} cross-sectional area is placed in a magnetic field of strength (H) 1000 Am^{- 1} . Then, the magnetic flux produced is (Susceptibility of material is 313 ) (Permeability of free space, μ_{0} = 4 π \times 10^{- 7} Hm^{- 1})$ (1) $8.33 \times 10^{- 8} Wb$ (2) $1.84 \times 10^{- 6} Wb$ (3) $9.87 \times 10^{- 6} Wb$ (4) $3.16 \times 10^{- 6} Wb$ 60. $The horizontal component of earth's magnetic field at a place is 3.5 \times 10^{- 5} T . A very long straight conductor carrying current of 2 A in the direction from South east to North West is placed. The force per unit length experienced by the conductor is....... \times 10^{- 6} N / m .$