JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank

done Mock Test - Magnetics Total Questions - 25

• question_answer1)
  In the following figure a wire bent in the form of a regular polygon of n sides is inscribed in a circle of radius\[a\]. Net magnetic field at centre will be
  A)
  \[\frac{{{\mu }_{0}}i}{2\pi a}\tan \frac{\pi }{n}\]                        done clear
  B)
  \[\frac{{{\mu }_{0}}ni}{2\pi a}\tan \frac{\pi }{n}\] done clear
  C)
  \[\frac{2}{\pi }\frac{ni}{a}{{\mu }_{0}}\tan \frac{\pi }{n}\]         done clear
  D)
  \[\frac{ni}{2a}{{\mu }_{0}}\tan \frac{\pi }{n}\] done clear
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• question_answer2)
  An electron is launched with velocity \[\vec{v}\] in a uniform magnetic field\[\vec{B}\]. The angle \[\theta \] between \[\vec{v}\] and \[\vec{B}\] lies between 0 and\[\pi /2\]. Its velocity vector \[\vec{v}\] returns to its initial value in a time interval of
  A)
  \[\frac{2\pi m}{eB}\]      done clear
  B)
  \[\frac{2\times 2\pi m}{eB}\] done clear
  C)
  \[\frac{\pi m}{eB}\]        done clear
  D)
  Depends upon angle between \[\vec{v}\] and \[\vec{B}\] done clear
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• question_answer3)
  Figure shows an equilateral triangle ABC of side \[l\]carrying currents as shown, and placed in a uniform magnetic field B perpendicular to the plane of triangle. The magnitude of magnetic force on the triangle is
  A)
  \[ilb\]                 done clear
  B)
  \[2ilb\] done clear
  C)
  \[3\,ilb\]             done clear
  D)
  Zero done clear
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• question_answer4)
  Two wires AO and OC carry equal currents i as shown in figure. One end of both the wires extends to infinity. Angle AOC is\[\alpha \]. The magnitude of magnetic field at point P on the bisector of these two wires at a distance r from point O is
  A)
  \[\frac{{{\mu }_{0}}}{2\pi }\frac{i}{r}\cot \left( \frac{\alpha }{2} \right)\] done clear
  B)
  \[\frac{{{\mu }_{0}}}{4\pi }\frac{i}{r}\cot \left( \frac{\alpha }{2} \right)\] done clear
  C)
  \[\frac{{{\mu }_{0}}}{4\pi }\frac{i}{r}\frac{\left( 1+\cos \frac{\alpha }{2} \right)}{\sin \left( \frac{\alpha }{2} \right)}\] done clear
  D)
  \[\frac{{{\mu }_{0}}}{4\pi }\frac{i}{r}\left( \frac{\alpha }{2} \right)\] done clear
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• question_answer5)
  An infinitely long current carrying wire carries current i. A charge of mass m and charge q is projected with speed v parallel to the direction of current at a distance r from it. Then, the radius of curvature at the point of projection is
  A)
  \[\frac{2rmv}{q{{\mu }_{0}}i}\] done clear
  B)
  \[\frac{2\pi rmv}{q{{\mu }_{0}}i}\] done clear
  C)
   r done clear
  D)
  Cannot be determined done clear
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• question_answer6)
  As shown in the figure, a three-sided frame is pivoted at P and Q and hangs vertically. Its sides are of same length and have a linear density of \[\sqrt{3}\] kg/m. A current of \[10\sqrt{3}\] A is sent through the frame, which is in a uniform magnetic field of 2T directed upwards as shown. Then angle through which the frame will be deflected in equilibrium is \[(Take\,g=10\,m/{{s}^{2}})\]
  A)
  \[{{30}^{0}}\]             done clear
  B)
  \[{{45}^{0}}\] done clear
  C)
  \[{{60}^{0}}\]             done clear
  D)
  \[{{90}^{0}}\] done clear
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• question_answer7)
  Two long conductors, separated by a distance d, carry currents\[{{I}_{1}}\] and \[{{I}_{2}}\] in the same direction. They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3d. The new value of the force between them is
  A)
  \[-2F\]    done clear
  B)
  \[F/3\] done clear
  C)
  \[-2F/3\] done clear
  D)
  \[-F/3\] done clear
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• question_answer8)
  A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields \[\vec{E}\] and \[\vec{B}\] with a velocity \[\vec{v}\] perpendicular to both \[\vec{E}\] and\[\vec{B}\], and comes out without any change in magnitude or direction of\[\vec{v}\]. Then
  A)
  \[\vec{v}=\frac{\vec{B}\times \vec{E}}{{{E}^{2}}}\]    done clear
  B)
  \[\vec{v}=\frac{\vec{E}\times \vec{B}}{{{B}^{2}}}\] done clear
  C)
  \[\vec{v}=\frac{\vec{B}\times \vec{E}}{{{B}^{2}}}\]   done clear
  D)
  \[\vec{v}=\frac{\vec{E}\times \vec{B}}{{{E}^{2}}}\] done clear
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• question_answer9)
  A dip needle lies initially in the magnetic meridian when it shows an angle of dip \[\theta \] at a place. The dip circle is rotated through an angle \[x\] in the horizontal plane and then it shows an angle of dip\[\theta '\]. Then \[\frac{\tan \theta '}{\tan \theta }\]is
  A)
  \[\frac{1}{\cos x}\]         done clear
  B)
  \[\frac{1}{\sin x}\] done clear
  C)
  \[\frac{1}{\tan x}\]         done clear
  D)
  \[\cos x\] done clear
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• question_answer10)
  A small rod of bismuth is suspended freely between the poles of a strong electromagnet. It is found to arrange itself at right angles to the magnetic field. This observation establishes that bismuth is
  A)
  Diamagnetic       done clear
  B)
  Paramagnetic done clear
  C)
  Fern-magnetic done clear
  D)
  Antiferro-magnetic done clear
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• question_answer11)
  A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a plane where dip angle is \[30{}^\circ \] and 15 oscillations per minute at a place where dip angle is \[60{}^\circ \]. The ratio of earth's magnetic field at two places is
  A)
  \[3\sqrt{3:}8\]    done clear
  B)
  \[16:9\sqrt{3}\] done clear
  C)
  \[4:9\]                done clear
  D)
  \[2\sqrt{2}:3\] done clear
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• question_answer12)
  The materials suitable for making electromagnets should have
  A)
  High retentivity and high coercivity done clear
  B)
  Low retentivity and low coercivity done clear
  C)
  High retentivity and low coercivity done clear
  D)
  Low retentivity and high coercivity. done clear
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• question_answer13)
  A thin bar magnet of length 2 L is bent at the mid-point so that the angle between them is\[60{}^\circ \]. The new length of the magnet is
  A)
  \[\sqrt{2}\,L\]     done clear
  B)
  \[\sqrt{3}\,L\] done clear
  C)
  \[2\,L\]              done clear
  D)
  \[L\] done clear
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• question_answer14)
  An electron is revolving in a circular orbit of radius r in a hydrogen atom. The angular momentum of the electron is The dipole moment associated with it is
  A)
  \[(2e/m)\,l\]        done clear
  B)
  \[(e/2m)\,l\] done clear
  C)
  \[(e/m)\,l\]          done clear
  D)
  \[(2m\text{/}e)\,l\] done clear
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• question_answer15)
  A charged particle moves through a magnetic field perpendicular to its direction. Then
  A)
  Both momentum and kinetic energy of the particle are not constant. done clear
  B)
  Both momentum and kinetic energy of the particle are constant. done clear
  C)
  Kinetic energy changes but the momentum remains constant. done clear
  D)
  The momentum changes but kinetic energy remains constant. done clear
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• question_answer16)
  A loop of flexible conducting wire of length \[l\] lies in magnetic field B which is normal to the plane of loop. A current is passed through the loop. The tension I developed in the wire to open up is
  A)
  \[\frac{\pi }{2}BIl\]         done clear
  B)
  \[\frac{BIl}{2}\] done clear
  C)
  \[\frac{BIl}{2\pi }\]         done clear
  D)
  \[BIl\]   done clear
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• question_answer17)
  An electric field acts along positive x-axis. A charged particle of charge q and mass m is released from origin and moves with velocity\[\vec{v}={{v}_{0}}\hat{j}\] under the action of electric' field and magnetic field, \[\vec{B}={{B}_{0}}\hat{i}\]. The velocity of particle becomes 2\[{{v}_{0}}\] after time\[\frac{\sqrt{3}m{{v}_{0}}}{\sqrt{2}q{{E}_{0}}}\]. Find the electric field.
  A)
  \[\frac{\sqrt{2}}{\sqrt{3}}{{E}_{0}}\hat{i}\]       done clear
  B)
  \[\frac{\sqrt{3}}{\sqrt{2}}{{E}_{0}}\hat{i}\] done clear
  C)
  \[\sqrt{3}{{E}_{0}}\hat{i}\]       done clear
  D)
  \[\sqrt{2}{{E}_{0}}\hat{i}\] done clear
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• question_answer18)
  Two identical particles having the same mass m and charges \[+q\] and \[-q\] separated by a distance d enter a uni-form magnetic field B directed perpendicular to paper inwards with speeds \[{{v}_{1}}\] and \[{{v}_{2}}\] as shown in figure. The particles will not collide if
  A)
  \[d>\frac{m}{Bq}({{v}_{1}}+{{v}_{2}})\] done clear
  B)
  \[d<\frac{m}{Bq}({{v}_{1}}+{{v}_{2}})\] done clear
  C)
  \[d>\frac{2m}{Bq}({{v}_{1}}+{{v}_{2}})\] done clear
  D)
  \[{{v}_{1}}={{v}_{2}}\] done clear
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• question_answer19)
  A ring of radius 5 m is lying in the x-y plane and is carrying current of 1 A in anti-clockwise sense. If a uniform magnetic field \[\vec{B}=3\hat{i}+4\hat{j}\] is switched on, then the  co-ordinates of point about which the loop will lift up is
  A)
  (3, 4)     done clear
  B)
  (4, 3) done clear
  C)
  (3, 0)     done clear
  D)
  (0, 3)      done clear
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• question_answer20)
      Three long, straight and parallel wires are arranged as shown in figure. The force experienced by 10 cm length of wire Q is
  A)
  \[1.4\times {{10}^{-4}}N\]towards the right done clear
  B)
  \[1.4\times {{10}^{-4}}N\]towards the left done clear
  C)
  \[2.6\times {{10}^{-4}}N\]towards the right done clear
  D)
  \[2.6\times {{10}^{-4}}N\]towards the left   done clear
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• question_answer21)
  A particle of specific charge \[q/m=\pi C\,k{{g}^{-1}}\] is projected from the origin toward positive \[x\]-axis with a velocity of \[10\,m\,{{s}^{-1}}\] in a uniform magnetic field\[\vec{B}=-2\hat{k}T\]. The velocity \[\vec{v}\] (in\[m{{s}^{-1}}\]) of particle after time t = 1/12 s will be 5\[\left[ \sqrt{M}i+j \right]\]. Find the value of M
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• question_answer22)
  A current of \[1/(4\pi )\] ampere is flowing in a long straight conductor. The line integral of magnetic induction around a closed path enclosing the current carrying conductor is\[N\times {{10}^{-7}}\,Wb\,{{m}^{-1}}\]. Fnd the value of TV?
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• question_answer23)
  A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through\[60{}^\circ \]. The torque required to maintain the needle in this position will be\[\sqrt{N\,}W\]. Find the value of N.
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• question_answer24)
  An iron rod of volume \[{{10}^{-4}}{{m}^{3}}\]and relative permeability1000 is placed inside a long solenoid wound with 5 turns/cm. If a current of 0.5 A is passed through the solenoid, then the magnetic moment (in\[A{{m}^{2}}\]) of the rod is_______.
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• question_answer25)
  Two identical magnetic dipoles of magnetic moments \[1.0A\text{-}{{m}^{2}}\] each, placed at a separation of 2 m with their axis perpendicular to each other. The resultant magnetic field at a point midway between the dipoles is\[\sqrt{M}\times {{10}^{-7}}\]. Find T the value of M.
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