Moving Charges & Magnetism PYQs Set 3 (PDF)

Set 3 of 17 · Questions 61-90 of 499

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Mere Teacher · Previous Year Questions NEET Physics · Moving Charges & Magnetism · Set 3 (Q61-90)
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61. $Magnetic field intensity at the center of the coil of 50 turns, radius 0. 5 m and carrying a current of 2 A, is$ (1) $3 \times 1 0^{- 5} T$ (2) $1.25 \times 1 0^{- 4} T$ (3) $0.5 \times 1 0^{- 5} T$ (4) $4 \times 1 0^{6} T$ 62. $A particle of mass m, charge Q and kinetic energy T enters in a transverse uniform magnetic field of induction B . After 3 seconds the kinetic energy of the particle will be$ (1) $T$ (2) $4 T$ (3) $3 T$ (4) $2T.$ 63. $A charged particle moves through a magnetic field in a direction perpendicular to it. Then the$ (1) $speed of the particle remains unchanged$ (2) $direction of the particle remains unchanged$ (3) $acceleration remains unchanged$ (4) $velocity remains unchanged.$ 64. $A charged particle is moving in a uniform magnetic field penetrates a layer of lead and thereby loses half of its kinetic energy, then the radius of curvature of its path is$ (1) $No change$ (2) $Reduced by \frac{1}{2} times of its initial values$ (3) $Reduced to \frac{1}{2} times of its initial values$ (4) $Reduce to \frac{1}{4} times of its initial values$ 65. $Two electrons, e_{1} and e_{2} of mass m and charge q are injected into the perpendicular direction of the magnetic field B such that the kinetic energy of e_{1} is double than that of e_{2} . The relation of their frequencies of rotation, f_{1} and f_{2} is$ (1) $f_{1} = f_{2}$ (2) $f_{1} = 2 f_{2}$ (3) $2 f_{1} = f_{2}$ (4) $4 f_{1} = f_{2}$ 66. $A circular coil of wire consisting of 100 turns each of radius 9 cm carries a current of 0.4 A . The magnitude of the magnetic field at the centre of coil is (μ_{0} = 12.56 \times 10^{- 7}) S.I. unit]$ (1) $2.4 \times 10^{- 11} T$ (2) $2.79 \times 10^{- 5} T$ (3) $2.79 \times 10^{- 4} T$ (4) $2.79 \times 10^{- 3} T$ 67. $A hoop and a solid cylinder of same mass and radius are made of a permanent magnetic material with their magnetic moment parallel to their respective axes. But the magnetic moment of hoop is twice of solid cylinder. They are placed in a uniform magnetic field in such a manner that their magnetic moments make a small angle with the field. If the oscillation periods of hoop and cylinder are T_{h} and T_{c} respectively, then:$ (1) $T_{h} = T_{c}$ (2) $T_{h} = 2 T_{c}$ (3) $T_{h} = 1.5 T_{c}$ (4) $T_{h} = 0.5 T_{c}$ 68. $The magnetic field due to current carrying a circular loop of radius 5 cm at a point on the axis at a distance of 12 cm from the centre is 250 μT . The magnetic field at the centre of the loop is$ (1) $2529 μT$ (2) $4394 μT$ (3) $1759 μT$ (4) $2908 μT$ 69. $An α -particle and a proton moving with the same kinetic energy enter a region of uniform magnetic field at right angles to the field. The ratio of the radii of the paths of α -particle to that of the proton is$ (1) $1 : 1$ (2) $1 : 2$ (3) $1 : 4$ (4) $1 : 8$ 70. $A moving coil galvanometer is converted into an ammeter of range 0 to 5 mA . The galvanometer resistance is 90Ω and the shunt resistance has a value of 10Ω . If there are 50 divisions in the galvanometer-turnedammeter on either sides of zero, its current sensitivity is$ (1) $2 \times 10^{4} div / A$ (2) $1 \times 10^{5} A / div$ (3) $2 \times 10^{4} A / div$ (4) $1 \times 10^{5} div / A$ 71. $A cylindrical conductor of radius R is carrying a constant current. The plot of the magnitude of the magnetic field, B with the distance, d from the center of the conductor, is correctly represented by the figure$ (1) (2) (3) (4) 72. $The number of turns in a coil of Galvanometer is tripled, then$ (1) $Both voltage and current sensitivity remains constant$ (2) $Voltage sensitivity increases 3 times and current sensitivity remains constant$ (3) $Both voltage and current sensitivity decrease by 33 %$ (4) $Voltage sensitivity remains constant and current sensitivity increases 3 times.$ 73. $A wire of length L meter carrying a current of I ampere is bent in the form of a circle. Its magnetic moment is [NEET 2020]$ (1) $(I L^{2} /4) Am^{2}$ (2) $(Iπ L^{2} /4) Am^{2}$ (3) $(2 I L^{2} / π) Am^{2}$ (4) $(I L^{2} /4 π) Am^{2}$ 74. $A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a plane perpendicular to magnetic field B . The kinetic energy of the proton that describes a circular orbit of radius 0.5 metre in the same plane with the same B is$ (1) $25 keV$ (2) $50 keV$ (3) $200 keV$ (4) $100 keV$ 75. $A thin ring of radius R meter has charge q coulomb uniformly spread on it. The ring rotates about its axis with a constant frequency of f revolutions/s. The value of magnetic induction in Wb/ m^{2} at the center of the ring is$ (1) $\frac{μ _{0} qf}{2 πR}$ (2) $\frac{μ _{0} q}{2 πfR}$ (3) $\frac{μ _{0} q}{2 fR}$ (4) $\frac{μ _{0} qf}{2 R}$ 76. $A magnet of total magnetic moment 10^{- 2} i A - m^{2} is placed in a time varying magnetic field, B i (cos ωt) where B = 1 Tesla and ω = 0.125 rad / s The work done for reversing the direction of the magnetic moment at T = 1 second, is:$ (1) $0.02 J$ (2) $0.007 J$ (3) $0.028 J$ (4) $0.014 J$ 77. $Acceleration of a charged particle of charge ' q' and mass ' m' moving in a uniform electric field of strength ' E' is$ (1) $\frac{qE}{m}$ (2) $\frac{m}{qE}$ (3) $mqE$ (4) $\frac{q}{mE}$ 78. $Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the centre of the ring is$ (1) $\frac{μ _{0} qf}{2 R}$ (2) $\frac{μ _{0} q}{2 fR}$ (3) $\frac{μ _{0} q}{2 πfR}$ (4) $\frac{μ _{0} qf}{2 πR}$ 79. $Torque acting on a rectangular coil carrying current I situated parallel to magnetic field of induction B having number of turns n and area A is$ (1) $nI (A \cdot B)$ (2) $\frac{nBA}{I}$ (3) $nI (A \times B)$ (4) $\frac{IBA}{n}$ 80. $A straight wire of mass 200 g and length 1.5 m carries a current of 2 A . It is suspended in mid-air by a uniform horizontal magnetic field B . The magnitude of B (in tesla) is (assume g = 9.9 m s^{- 2})$ (1) $2$ (2) $1.5$ (3) $0.55$ (4) $0.66$ 81. $Two parallel conductors carrying unequal currents in the same direction$ (1) $neither attract nor repel each other$ (2) $repel each other$ (3) $attract each other$ (4) $will have rotational motion.$ 82. $It is found that a non-zero current element is unable to produce any magnetic field at a particular point. Then the angle between the current element and the position vector of that point with respect to the current element is$ (1) $must be 45^{\circ}$ (2) $may be 0^{\circ} or 180^{\circ}$ (3) $must be 90^{\circ}$ (4) $may be 30^{\circ} to 60^{\circ}$ 83. $A short bar magnet of magnetic moment 0.4J T^{-1} is place in a uniform magnetic field of 0.16 T. The magnet is in stable equilibrium when the potential energy is:$ (1) $-0.064 J$ (2) $zero$ (3) $- 0.082 J$ (4) $0.064$ 84. $A galvanometer of resistance 50Ω is connected to a battery of 3 V along with a resistance of 2950Ω in series shows full-scale deflection of 30 divisions. The additional series resistance required to reduce the deflection to 20 divisions is$ (1) $4440Ω$ (2) $1500Ω$ (3) $7400Ω$ (4) $2950Ω$ 85. $A galvanometer coil has a resistance of 15 ohm and gives full scale deflection for a current of 4 mA . To convert it to an ammeter of range 0 to 6 A,$ (1) $10 mΩ resistance is to be connected in parallel to the galvanometer$ (2) $10 mΩ resistance is to be connected in series with the galvanometer$ (3) $0.1Ω resistance is to be connected in parallel to the galvanometer$ (4) $0.1Ω resistance is to be connected in series with the galvanometer.$ 86. $If a velocity has both perpendicular and parallel components while moving through a magnetic field, what is the path followed by a charged particle?$ (1) $Linear$ (2) $Circular$ (3) $Helical$ (4) $Elliptical$ 87. $A charge q moves in a region where electric field and magnetic field both exist, then force on it is$ (1) $q (v \times B) .$ (2) $q E + q (v \times B)$ (3) $q E + q (B \times v)$ (4) $q B + q (E \times v)$ 88. $A proton and a deutron (q = + e, m = 2.0 u) having same kinetic energies enter a region of uniform magnetic field B, moving perpendicular to B . The ratio of the radius r_{d} of deutron path to the radius r_{p} of the proton path is:$ (1) $2 : 1$ (2) $1 : 1$ (3) $1 : 2$ (4) $1 : 2$ 89. $An electron (mass m) is accelerated through a potential difference of ' V' and then it enters in a magnetic field of induction ' B' normal to the lines. The radius of the circular path is (e = electronic charge)$ (1) $\frac{2 eV}{m}$ (2) $\frac{2 Vm}{e B ^{2}}$ (3) $\frac{2 Vm}{eB}$ (4) $\frac{2 Vm}{e ^{2} B}$ 90. $A charged particle is moving in a magnetic field of strength B perpendicular to the direction of the field. If q and m denote the charge and mass of the particle respectively, then the frequency of rotation of the particle is$ (1) $f = \frac{qB}{2 πm}$ (2) $f = \frac{qB}{2 π m ^{2}}$ (3) $f = \frac{2 π ^{2} m}{qB}$ (4) $f = \frac{2 πm}{qB}$