Moving Charges & Magnetism PYQs Set 2 (PDF)

Set 2 of 19 · Questions 31-60 of 549

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Mere Teacher · Previous Year Questions JEE Main Physics · Moving Charges & Magnetism · Set 2 (Q31-60)
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31. $A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of magnetic field will be equal to$ (1) $B$ (2) $2 B$ (3) $4 B$ (4) $\frac{B}{2}$ 32. $Two long straight wires P and Q carrying equal current 10A each were kept parallel to each other at 5 cm distance. Magnitude of magnetic force experienced by 10 cm length of wire P is F_{1} . If distance between wires is halved and currents on them are doubled, force F_{2} on 10 cm length of wire P will be:$ (1) $8 F_{1}$ (2) $10 F_{1}$ (3) $F_{1} /8$ (4) $F_{1} /10$ 33. $A solenoid of 1000 turns per metre has a core with relative permeability 500 . Insulated windings of thesolenoid carry an electric current of 5 A . The magnetic flux density produced by the solenoid is:(permeability of free space (= 4 π \times 10^{- 7} H / m)$ (1) $πT$ (2) $2\times 1 0^{- 3} πT$ (3) $\frac{π}{5} T$ (4) $10^{- 4} πT$ 34. $The magnetic field at the center of a current carrying circular loop of radius R is 16 μ T . The magnetic field at a distance x = 3 R on its axis from the centre is____μT .$ (1) $4$ (2) $2$ (3) $22$ (4) $8$ 35. $A uniform magnetic field acts right angles to the direction of motion of electrons. As a result, the electron moves in a circular path of radius 2 cm. If the speed of electrons is doubled, then the radius of the circular path will be$ (1) $2.0 cm$ (2) $0.5 cm$ (3) $4.0 cm$ (4) $1.0 cm$ 36. $A long wire is bent into a circular coil of one turn and then into a circular coil of smaller radius having n turns. If the same current passes in both the cases, the ratio of magnetic fields produced at the centre for one turn to that of n turns is$ (1) $1 : n$ (2) $n : 1$ (3) $1 : n^{2}$ (4) $n^{2} : 1$ 37. $A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 \times 1 0^{- 4} ampere gives a deflection of one division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of$ (1) $2500 Ω as a shunt$ (2) $2450 Ω as a shunt$ (3) $2550 Ω in series$ (4) $2450 Ω in series.$ 38. $An alternating electric field, of frequency v, is applied across the dees (radius = R) of a cyclotron that is being used to accelerate protons (mass = m). The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by:$ (1) $B = m ve and K = 2 m π^{2} v^{2} R^{2}$ (2) $B = \frac{2 πmv}{e} and K = m^{2} πv R^{2}$ (3) $B = \frac{2 πmv}{e} and K = 2 m π^{2} v^{2} R^{2}$ (4) $B = \frac{mv}{e} and K = m^{2} πv R^{2}$ 39. $A straight wire carrying a current (I) is turned into a circular loop. If the magnitude of the magnetic moment associated with it is ' M', then the length of the wire will be$ (1) $\frac{Mπ}{4 I}$ (2) $(\frac{4 πI}{M})^{\frac{1}{2}}$ (3) $(\frac{4 Mπ}{I})^{\frac{1}{2}}$ (4) $4 πMI$ 40. $A charge having elm equal to 1 0^{8} C / kg and with velocity 3 \times 1 0^{5} m / s enters into a uniform magnetic field B = 0.3 tesla at an angle 3 0^{o} with direction of field. The radius of curvature will be$ (1) $0.01 cm$ (2) $0.5 cm$ (3) $1 cm$ (4) $2 cm.$ 41. $A small circular loop of conducting wire has radius a and carries current I . It is placed in a uniform magnetic field B perpendicular to its plane such that when rotated slightly about its diameter and released, it starts performing simple harmonic motion of time period T . If the mass of the loop is m Then$ (1) $T = \frac{πm}{IB}$ (2) $T = \frac{2 m}{IB}$ (3) $T = \frac{πm}{2 IB}$ (4) $T = \frac{2 πm}{IB}$ 42. $Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): A electron in a certain region of uniform magnetic field is moving with constant velocity in a straight line path. Reason (R): The magnetic field in that region is along the direction of velocity of the electron. choose the correct answer from the options given below:$ (1) $(A) is true but (R) is false$ (2) $Both (A) and (R) are true but (R) is not the correct explanation of (A)$ (3) $Both (A) and (R) are true and (R) is the correct explanation of A$ (4) $(A) is false but (R) is true$ 43. $The magnitude of magnetic induction at a point on the axis at a large distance (r) from the centre of circular coil of ' n' turns, and area ' A' carrying current (I) is given by$ (1) $B_{axis} = \frac{μ _{0}}{4 π} \cdot \frac{nA}{I r ^{3}}$ (2) $B_{axis} = \frac{μ _{0}}{4 π} \cdot \frac{2 nIA}{r ^{3}}$ (3) $B_{axis} = \frac{μ _{0}}{4 π} \cdot \frac{2 nI}{A r ^{3}}$ (4) $B_{axis} = \frac{μ _{0}}{4 π} \cdot \frac{nIA}{r ^{3}}$ 44. $A galvanometer coil has a resistance of 50Ω and the meter shows full scale deflection for a current of 5 mA . This galvanometer is converted into voltmeter of range 0 - 20 V by connecting$ (1) $3950Ω in series with galvanometer$ (2) $4050Ω in series with galvanometer$ (3) $3950Ω in parallel with galvanometer$ (4) $4050Ω in parallel with galvanometer$ 45. $A cyclotron is used to accelerate protons (_{1}^{1} H), Deuterons (_{1}^{2} H) and α -particles (_{2}^{4} He) . While exiting under similar conditions, the minimum K.E. is gained by$ (1) $deuteron$ (2) $same for all$ (3) $α -particle$ (4) $proton$ 46. $A proton and a deuteron with the same initial kinetic energy enter a magnetic field in a direction perpendicular to the direction of the field. The ratio of the radii of the circular trajectories described by them is$ (1) $1 : 4$ (2) $1 : 2$ (3) $1 : 1$ (4) $1 : 2 .$ 47. $A cyclotron is used to accelerate protons. If the operating magnetic field is 1.0 T and the radius of the cyclotron 'dees' is 60 cm, the kinetic energy of the accelerated protons in MeV will be: [use m_{p} = 1.6 x 1 0^{- 27} kg, e = 1.6 x 1 0^{- 19} C]$ (1) $12$ (2) $18$ (3) $16$ (4) $32$ 48. $A toroid has a core (non-ferro magnetic) of inner radius 24 cm and outer radius 26 cm around which 2000 turns of a wire is wound. If the current in the wire is 12 A, the magnetic field inside the core of the toroid is$ (1) $1.92 \times 10^{- 2} T$ (2) $1.88\times 1 0^{- 2} .T$ (3) $2.12 \times 10^{- 2} T$ (4) $1.98 \times 10^{- 2} T$ 49. $Two moving coil galvanometer, X and Y have coils with resistance 10Ω and 14Ω cross-sectional areas 4.8 \times 10^{- 3} m^{2} and 2.4 \times 10^{- 3} m^{2}, number of turns 30 and 45 respectively. They are placed in magnetic field of 0.25 T and 0.50 T respectively. Then, the ratio of their current sensitivities and the ratio of their voltage sensitivities are respectively$ (1) $2 : 3, 14 : 15$ (2) $5 : 7, 2 : 1$ (3) $2 : 13, 1 : 2$ (4) $14 : 15, 2 : 9$ 50. $In a galvanometer, 5 % of the total current in the circuit passes through it. If the resistance of the galvanometer is G, the shunt resistance S connected to the galvanometer is$ (1) $19 G$ (2) $\frac{G}{19}$ (3) $20 G$ (4) $\frac{G}{20}$ 51. $A proton is projected with a uniform velocity v along the axis of a current carrying solenoid, then$ (1) $the proton will be accelerated along the axis.$ (2) $the proton path will be circular about the axis.$ (3) $the proton moves along helical path.$ (4) $the proton will continue to move with velocity v along the axis.$ 52. $A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be:$ (1) $2 n^{2} B$ (2) $nB$ (3) $n^{2} B$ (4) $2nB$ 53. $A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV the energy acquired by the alpha particle will be$ (1) $0.5 MeV$ (2) $1.5 MeV$ (3) $1 MeV$ (4) $4 MeVs$ 54. $A cyclotron's oscillator frequency is 20 MHz . The operating magnetic field for accelerating protons is (charge of proton = 1.6 \times 10^{- 19} C, mass of proton = 1.67 x 10^{- 27} kg)$ (1) $0.66 T$ (2) $1.1 T$ (3) $0.33 T$ (4) $1.31 T$ 55. $Current sensitivity of a moving coil galvanometer is 5 div / mA and its voltage sensitivity (angular deflection per unit voltage applied) is 20 div / V . The resistance of the galvanometer is [NEET 2018]$ (1) $250Ω$ (2) $25Ω$ (3) $40Ω$ (4) $500Ω$ 56. $A straight current carrying conductor is kept along the axis of circular loop carrying current. The force exerted by the straight conductor on the loop is$ (1) $perpendicular to the plane of the loop$ (2) $in the plane of the loop, away from the center$ (3) $in the plane of the loop, towards the center$ (4) $zero$ 57. $A current of (\frac{2}{3}) A produces a deflection of 60^{\circ} in a tangent galvanometer. The reduction factor is$ (1) $(\frac{2}{3}) A$ (2) $(\frac{2}{3}) A$ (3) $2 A$ (4) $(\frac{3}{2}) A$ 58. $Sensitivity of a moving coil galvanometer can be increased by$ (1) $decreasing the number of turns of coil$ (2) $increasing the number of turns of coil$ (3) $decreasing the area of a coil$ (4) $by using a weak magnet$ 59. $A closely wounded circular coil of radius 5 cm produces a magnetic field of 37.68 x 10-4 T at its center. The current through the coil is _________A. [Given, number of turns in the coil is 100 and π = = 3.14]$ 60. $An electron with kinetic energy 5 eV enters a region of uniform magnetic field of 3 μT perpendicular to its direction. An electric field E is applied perpendicular to the direction of velocity and magnetic field. The value of E, so that electron moves along the same path, is_____NC^{- 1} . ( Given, mass of electron = 9 \times 10^{- 31} kg, electric charge = 1.6 \times 10^{- 19} C)$