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

done Self Evaluation Test - Moving Charges and Mangetism Total Questions - 100

• question_answer1)
  A charged particle of mass m and charge q travels on a circular path of radius r that is perpendicular to a magnetic field B. The time taken by the particle to complete one revolution is
  A)
  \[\frac{2\pi {{q}^{2}}B}{m}\] done clear
  B)
  \[\frac{2\pi mq}{B}\] done clear
  C)
  \[\frac{2\pi m}{qB}\] done clear
  D)
  \[\frac{2\pi qB}{m}\] done clear
  View Solution play_arrow

• question_answer2)
  A charged particle enters in a magnetic field in a direction perpendicular to the magnetic field. Which of the following graphs show the correct variation of kinetic energy of the particle with time t?
  A)
  done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
  View Solution play_arrow

• question_answer3)
  An electric charge \[+q\] moves with velocity \[10m{{s}^{-1}}\]in an electromagnetic field given by \[\overset{\to }{\mathop{E}}\,=3\hat{i}+\hat{j}+2\hat{k}\] and \[\overset{\to }{\mathop{B}}\,=\hat{i}+\hat{j}-3\hat{k}\] The y- component of the force experienced by \[+q\] is:
  A)
  \[11\,\,q\] done clear
  B)
  \[5\,q\] done clear
  C)
  \[3\,q\] done clear
  D)
  \[2\,q\] done clear
  View Solution play_arrow

• question_answer4)
  A beam of electrons is moving with constant velocity in a region having simultaneous perpendicular electric and magnetic fields of strength \[20\,V{{m}^{-1}}\] and 0.5 T respectively at right angles to the direction of motion of the electrons. Then the velocity of electrons must be
  A)
  \[8\,m/s\] done clear
  B)
  \[20\,m/s\] done clear
  C)
  \[40\,m/s\] done clear
  D)
  \[\frac{1}{40}\,m/s\] done clear
  View Solution play_arrow

• question_answer5)
  Two electron beams having their velocities in the ratio 1 : 2 are subjected to identical magnetic fields acting at right angles to the direction of motion of electron beams. The ratio of deflection produced is:
  A)
  2 : 1  done clear
  B)
  1 : 2   done clear
  C)
  4 : 1  done clear
  D)
  1 : 4 done clear
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• question_answer6)
  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
  A)
  \[\frac{{{\mu }_{0}}qf}{2R}\] done clear
  B)
  \[\frac{{{\mu }_{0}}q}{2f\,R}\] done clear
  C)
  \[\frac{{{\mu }_{0}}q}{2\pi f\,R}\] done clear
  D)
  \[\frac{{{\mu }_{0}}qf}{2\pi \,R}\] done clear
  View Solution play_arrow

• question_answer7)
  A charged particle moves insides a pipe which is bent as shown in fig. If \[R>\frac{mv}{qB}\], then force exerted by the pipe on charged particle at P is (Neglect gravity)        
  A)
  toward center done clear
  B)
  away from center done clear
  C)
         zero done clear
  D)
  none of these     done clear
  View Solution play_arrow

• question_answer8)
  A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in uniform magnetic field. What should be the energy of an a-particle to describe a circle of same radius in the same field?
  A)
  2 MeV done clear
  B)
  1 MeV done clear
  C)
  0.5 MeV done clear
  D)
  4 MeV done clear
  View Solution play_arrow

• question_answer9)
  Under the influence of a uniform magnetic field a charged particle is moving in a circle of radius R with constant speed v The time period of the motion
  A)
  depends on both R and v done clear
  B)
  is independent of both R and v done clear
  C)
  depends on R and not on v done clear
  D)
  depends on v and not on R done clear
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• question_answer10)
  In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular path of radius R using a magnetic field B. If V and B are kept constant, the \[ratio\,\left( \frac{ch\operatorname{arge}\,on\,the\,ion}{mass\,of\,the\,ion} \right)\] will be proportional to
  A)
  \[1/{{R}^{2}}\]            done clear
  B)
  \[{{R}^{2}}\]    done clear
  C)
  R          done clear
  D)
  \[1/R\] done clear
  View Solution play_arrow

• question_answer11)
  An ionized gas contains both positive and negative ions. If it is subjected simultaneously to an electric field along the \[+x\]-direction and a magnetic field along the \[+z\]-direction, then
  A)
  positive ions deflect towards \[+y\]-direction and negative ions towards -y direction done clear
  B)
  all ions deflect towards \[+y\]-direction done clear
  C)
  all ions deflect towards \[~-y\]-direction done clear
  D)
  positive ions deflect towards \[~-y\]-direction and negative ions towards \[~+y\]-direction. done clear
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• question_answer12)
  Three particles, an electron (e), a proton (p) and a helium atom (He) are moving in circular paths with constant speeds in the x - y plane in a region where a uniform magnetic field B exists along z - axis. The times taken bye, p and He inside the field to complete one revolution are \[{{t}_{e}}\], \[{{t}_{p}}\] and \[{{t}_{He}}\] respectively. Then,   
  A)
  \[{{t}_{He}}>{{t}_{p}}={{t}_{e}}\]    done clear
  B)
  \[{{t}_{He}}>{{t}_{p}}>{{t}_{e}}\] done clear
  C)
  \[{{t}_{He}}={{t}_{p}}={{t}_{e}}\]    done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer13)
       A particle of specific charge \[\frac{q}{m}=\pi \,\,Ck{{g}^{-1}}\]is projected from the origin towards positive x-axis with a velocity of \[10m{{s}^{-1}}\] in a uniform magnetic field \[\overset{\to }{\mathop{B}}\,=-2\hat{k}\,T\] . The velocity \[\overrightarrow{v}\]of particle after time = 1/12 s will be \[(in\,m{{s}^{-1}})\]
  A)
  \[5[\hat{i}+\sqrt{3}\hat{j}]\]     done clear
  B)
         \[5[\sqrt{3}\hat{i}+\hat{j}]\] done clear
  C)
  \[5[\sqrt{3\hat{i}}-\hat{j}]\]      done clear
  D)
         \[5[\hat{i}-\hat{j}]\] done clear
  View Solution play_arrow

• question_answer14)
  A particle is projected in a plane perpendicular to a uniform magnetic field. The area bounded by the path described by the particle is proportional to
  A)
  the velocity      done clear
  B)
         the momentum done clear
  C)
  the kinetic energy            done clear
  D)
  None of these done clear
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• question_answer15)
  Consider a hypothetic spherical body. The body is cut into two parts about the diameter. One of hemispherical portion has mass distribution m whie the other portion has identical charge distribution q. The body is rotated about the axis       with constant speed o. Then, the ratio of magnetic moment to angular momentum is  
  A)
  \[\frac{q}{2m}\] done clear
  B)
  \[>\frac{q}{2m}\] done clear
  C)
  \[<\frac{q}{2m}\]          done clear
  D)
  cannot be calculated done clear
  View Solution play_arrow

• question_answer16)
  There exist uniform magnetic and electric fields of magnitudes 1T and \[1\,V\,{{m}^{-1}}\], respectively, along positive y-axis. A charged particle of mass 1 kg and charge 1 C is having velocity \[1\,\,m\,{{s}^{-1}}\] along x-axis and is at origin at t=0. Then, the coordinates of the particles at time \[\pi s\] will be
  A)
  \[(0,\,\,1,\,\,2)m\]            done clear
  B)
  \[(0,\,-{{\pi }^{2}},\,-2)m\] done clear
  C)
  \[(2,\,{{\pi }^{2}}/2,\,2)m\]      done clear
  D)
         \[(0,\,\,{{\pi }^{2}}/2,\,\,2)m\] done clear
  View Solution play_arrow

• question_answer17)
  A particle of mass m and charge q moves with a constant velocity v along the positive x-direction. It enters a region containing a uniform magnetic field B directed along the negative z-direction, extending from \[x=a\] to \[~x=b\]. The minimum value of v required so that the particle can just enter the region x > b is
  A)
  \[\frac{qbB}{m}\]          done clear
  B)
  \[\frac{q(b-a)B}{m}\] done clear
  C)
  \[\frac{qaB}{m}\]          done clear
  D)
  \[\frac{q(b+a)B}{2m}\] done clear
  View Solution play_arrow

• question_answer18)
  For a positively charged particle moving in a x-y plane initially along the x-axis, there is a sudden change in its path due to the presence of electric and/or magnetic fields beyond P. The curved path is shown in the x-y plane and is found to be non- circular. Which one of the following combinations is possible?
  A)
  \[\overset{\to }{\mathop{E}}\,=0;\overset{\to }{\mathop{B}}\,=b\hat{i}+c\hat{k}\]          done clear
  B)
  \[\overset{\to }{\mathop{E}}\,=a\hat{i};\overset{\to }{\mathop{B}}\,=c\hat{k}+a\hat{i}\] done clear
  C)
  \[\overset{\to }{\mathop{E}}\,=0;\overset{\to }{\mathop{B}}\,=c\hat{j}+b\hat{k}\]          done clear
  D)
  \[\overset{\to }{\mathop{E}}\,=a\hat{i};\overset{\to }{\mathop{B}}\,=c\hat{k}+b\hat{j}\] done clear
  View Solution play_arrow

• question_answer19)
  Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii \[{{R}_{1}}\]and \[{{R}_{2}}\] respectively. The ratio of the mass of X to that of Y is
  A)
  \[{{({{R}_{1}}/{{R}_{2}})}^{1/2}}\]               done clear
  B)
  \[{{R}_{2}}/{{R}_{1}}\] done clear
  C)
  \[{{({{R}_{1}}/{{R}_{2}})}^{2}}\]                  done clear
  D)
  \[{{R}_{1}}/{{R}_{2}}\] done clear
  View Solution play_arrow

• question_answer20)
  A uniform magnetic field of magnitude IT exists in       region y>0 is along k direction as shown. A particle of charge 1 C is projected from point \[(-\sqrt{3},-1)\]  towards origin with speed 1 m/sec. If mass of particle is 1 kg, then co-ordinates of centre of circle in which particle moves are-                
  A)
  \[(1,\,\sqrt{3})\] done clear
  B)
  \[(1,\,-\sqrt{3})\] done clear
  C)
  \[\left( \frac{1}{2},-\frac{\sqrt{3}}{2} \right)\] done clear
  D)
  \[\left( \frac{\sqrt{3}}{2},-\frac{1}{2} \right)\] done clear
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• question_answer21)
  An electron, charge?e, mass m, enters a uniform magnetic field \[\overset{\to }{\mathop{B}}\,=B\overset{\to }{\mathop{i}}\,\] with an initial velocity \[\overset{\to }{\mathop{v}}\,={{v}_{x}}\overset{\to }{\mathop{i}}\,+{{v}_{y}}\overset{\to }{\mathop{j}}\,\]. What is the velocity of the electron after a time interval of t second?
  A)
  \[{{v}_{x}}\hat{i}+{{v}_{y}}\hat{j}+\frac{e}{m}{{v}_{y}}B\,t\,\hat{k}\]         done clear
  B)
  \[{{v}_{x}}\hat{i}+{{v}_{y}}\hat{j}-\frac{e}{m}{{v}_{y}}B\,t\,\hat{k}\] done clear
  C)
  \[{{v}_{x}}\hat{i}+\left( {{v}_{y}}+\frac{e}{m}{{v}_{y}}B\,t\, \right)\hat{j}\]   done clear
  D)
  \[{{v}_{x}}\hat{i}+\left( {{v}_{y}}+\frac{e}{m}{{v}_{y}}B\,t\, \right)\hat{i}+{{v}_{y}}\hat{j}\] done clear
  View Solution play_arrow

• question_answer22)
              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 used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by:
  A)
  \[B=\frac{mv}{e}\]and \[K=2m{{\pi }^{2}}{{v}^{2}}{{R}^{2}}\] done clear
  B)
  \[B=\frac{2\pi mv}{e}\] and \[K={{m}^{2}}\pi v{{R}^{2}}\] done clear
  C)
  \[B=\frac{2\pi mv}{e}\] and \[K=2m{{\pi }^{2}}{{v}^{2}}{{R}^{2}}\] done clear
  D)
  \[B=\frac{mv}{e}\] and \[K={{m}^{2}}\pi v{{R}^{2}}\] done clear
  View Solution play_arrow

• question_answer23)
  A uniform magnetic field is directed out of the page. A charged particle, moving in  the plane of the page, follows a clockwise spiral of  decreasing radius as shown, A reasonable explanation is 
  A)
  the charge is positive and slowing down done clear
  B)
  the charge is negative and slowing down done clear
  C)
  the charge is positive and speeding up done clear
  D)
  the charge is negative and speeding up done clear
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• question_answer24)
  A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic induction \[{{10}^{-4}}Wb/{{m}^{2}}\] (=1.0 gauss). The orbital radius of the electron is
  A)
  12cm done clear
  B)
  16cm done clear
  C)
  11cm done clear
  D)
  18cm done clear
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• question_answer25)
  A deuteron of kinetic energy 50 ke V is describing a circular orbit of radius 0.5 metre in a plane perpendicular to the 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
  A)
  \[25\,ke\,V\]       done clear
  B)
  \[50\,ke\,V\] done clear
  C)
  \[200\,ke\,V\]      done clear
  D)
  \[100\,ke\,V\] done clear
  View Solution play_arrow

• question_answer26)
  A particle of charge q and mass m starts moving from the origin under the action of an electric field \[\overset{\to }{\mathop{E}}\,={{E}_{0}}\hat{i}\] and \[\overset{\to }{\mathop{B}}\,={{B}_{0}}\hat{i}\] with velocity \[\overset{\to }{\mathop{v}}\,={{v}_{0}}\hat{j}\] .The speed of the particle will become\[2{{v}_{0}}\] after time       
  A)
  \[t=\frac{2m{{v}_{0}}}{qE}\]   done clear
  B)
  \[t=\frac{2Bq}{m{{v}_{0}}}\] done clear
  C)
  \[t=\frac{\sqrt{3}Bq}{m{{v}_{0}}}\]     done clear
  D)
  \[t=\frac{\sqrt{3}m{{v}_{0}}}{qE}\] done clear
  View Solution play_arrow

• question_answer27)
  OABC is current carrying square loop an electron is projected from the centre of loop along its diagonal AC as shown. Unit vector in the direction of initial acceleration will be
  A)
  \[\hat{k}\]          done clear
  B)
  \[-\left( \frac{\hat{i}+\hat{j}}{\sqrt{2}} \right)\] done clear
  C)
  \[-\hat{k}\]         done clear
  D)
  \[\frac{\hat{i}+\hat{j}}{\sqrt{2}}\] done clear
  View Solution play_arrow

• question_answer28)
  Two identical particles having the same mass m     and charges +q and -q separated by a distance d    enter a uniform magnetic field B directed    perpendicular to paper inwards with in speeds \[{{v}_{1}}\]  and \[{{v}_{2}}\] as shown in Fig. 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
  View Solution play_arrow

• question_answer29)
  A charged sphere of mass m and charge - q starts sliding along the surface of a smooth hemispherical bowl, at position P. The region has a transverse uniform magnetic field B. Normal force by the surface of bowl on the sphere at position Q is           
  A)
  \[mg\,\sin \theta +qB\sqrt{2g\,R\,\sin \,\theta }\] done clear
  B)
  \[3\,mg\,\sin \theta +qB\sqrt{2g\,R\,\sin \,\theta }\] done clear
  C)
  \[mg\,\sin \theta -qB\sqrt{2g\,R\,\sin \,\theta }\] done clear
  D)
  \[3\,mg\,\sin \theta -qB\sqrt{2g\,R\,\sin \,\theta }\] done clear
  View Solution play_arrow

• question_answer30)
  A positive charge 'q' of mass 'm' is moving along the +x axis. We wish to apply a uniform magnetic field B for time \[\Delta \,t\] so that the charge reverses its direction crossing the y axis at a distance d. Then:
  A)
  \[B=\frac{mv}{qd}\] and \[\Delta t=\frac{\pi d}{v}\] done clear
  B)
  \[B=\frac{mv}{2qd}\]   and \[\Delta t=\frac{\pi d}{2v}\] done clear
  C)
  \[B=\frac{2mv}{qd}\] and \[\Delta t=\frac{\pi d}{2v}\] done clear
  D)
  \[B=\frac{2mv}{qd}\] and \[\Delta t=\frac{\pi d}{v}\] done clear
  View Solution play_arrow

• question_answer31)
  A cyclotron is operated at an oscillator frequency of 24 MHz and has a dee radius\[R=60cm\]. What is magnitude of the magnetic field B (in Tesla) to accelerate deuterons\[(mass=3.34\times {{10}^{-27}})kg\]?
  A)
  9.5 done clear
  B)
  7.2     done clear
  C)
  5.0  done clear
  D)
  3.2 done clear
  View Solution play_arrow

• question_answer32)
  Two particles, each of mass m and charge q, are attached to the two ends of a light rigid rod of length 1R. The rod is rotated at constant angular speed about a perpendicular axis passing through its centre. The ratio of the magnitudes of the magnetic moment of the system and its angular momentum about the centre of the rod is
  A)
  \[\frac{q}{2m}\] done clear
  B)
  \[\frac{q}{m}\] done clear
  C)
  \[\frac{2q}{m}\] done clear
  D)
  \[\frac{q}{\pi m}\] done clear
  View Solution play_arrow

• question_answer33)
  A charged particle of specific charge (charge/ mass) \[\alpha \] is released from origin at time t = 0 with velocity \[\overset{\to }{\mathop{v}}\,={{v}_{0}}(\hat{i}+\hat{j})\] in uniform magnetic field \[\overset{\to }{\mathop{B}}\,={{B}_{0}}\hat{i}\]. Coordinates of the particle at time  \[t=\pi /({{B}_{0}}\alpha )\]
  A)
  \[\left( \frac{{{v}_{0}}}{2{{B}_{0}}\alpha },\frac{\sqrt{2}{{v}_{0}}}{\alpha {{B}_{0}}},\frac{-{{v}_{0}}}{{{B}_{0}}\alpha } \right)\] done clear
  B)
  \[\left( \frac{-{{v}_{0}}}{2{{B}_{0}}\alpha },0,0 \right)\] done clear
  C)
  \[\left( 0,\frac{2{{v}_{0}}}{{{B}_{0}}\alpha },\frac{{{v}_{0}}\pi }{2{{B}_{0}}\alpha } \right)\] done clear
  D)
  \[\left( \frac{{{v}_{0}}\pi }{{{B}_{0}}\pi },0\frac{-2{{v}_{0}}}{{{B}_{0}}\alpha } \right)\] done clear
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• question_answer34)
  A particle of mass m and charge q enters a region of magnetic field (as shown) with speed v. There is a region in which the magnetic field is absent, as shown. The particle after entering the region collides elastically with a rigid wall. Time after which the velocity of particle becomes antiparallel  to its initial velocity is
  A)
  \[\frac{m}{2qB}(\pi +4)\] done clear
  B)
  \[\frac{m}{qB}(\pi +2)\] done clear
  C)
  \[\frac{m}{4qB}(\pi +2)\] done clear
  D)
  \[\frac{m}{4qB}(2\pi +3)\] done clear
  View Solution play_arrow

• question_answer35)
  The figure shows a thin metalic rod whose one end is pivoted at point 0. The rod rotates about the end O in a plane perpendicular to the uniform magnetic field with angular frequency \[\omega \] in clockwise direction. Which of the following is correct?             
  A)
  The free electrons of the rod move towards the outer end done clear
  B)
  The free electrons of the rod move towards the pivoted end. done clear
  C)
  The free electrons of the rod move towards the mid-point of the rod. done clear
  D)
  The free electrons of the rod do not move towards any end of the rod as rotation of rod has no effect on motion of free electrons. done clear
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• question_answer36)
  A helium nucleus makes a full rotation in a circle of radius 0.8 meter in 2 sec. The value of the magnetic field induction B in tesla at the centre of circle will be
  A)
  \[2\times {{10}^{-19}}{{\mu }_{0}}\]      done clear
  B)
         \[{{10}^{-19}}/{{\mu }_{0}}\] done clear
  C)
  \[{{10}^{-19}}{{\mu }_{0}}\]      done clear
  D)
  \[2\times {{10}^{-20}}/{{\mu }_{0}}\] done clear
  View Solution play_arrow

• question_answer37)
  The correct plot of the magnitude of magnetic field 5 vs distance r from centre of the wire is, if the radius of wire is R  
  A)
          done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
  View Solution play_arrow

• question_answer38)
  A current of I ampere flows in a wire forming a circular arc of radius r metres subtending an angle  \[\theta \] at the centre as shown. The magnetic field at the centre O in tesla is
  A)
  \[\frac{{{\mu }_{0}}I\theta }{4\pi r}\]     done clear
  B)
  \[\frac{{{\mu }_{0}}I\theta }{2\pi r}\] done clear
  C)
  \[\frac{{{\mu }_{0}}I\theta }{2r}\]          done clear
  D)
  \[\frac{{{\mu }_{0}}I\theta }{4r}\] done clear
  View Solution play_arrow

• question_answer39)
  The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is \[54\,\mu T\]. What will be its value at the centre of loop?              
  A)
  \[125\mu T\] done clear
  B)
  \[150\mu T\] done clear
  C)
  \[250\mu T\] done clear
  D)
  \[75\mu T\] done clear
  View Solution play_arrow

• question_answer40)
  If the magnetic field at P can be written as K tan \[\left( \frac{\alpha }{2} \right)\], then K
  A)
  \[\frac{{{\mu }_{0}}I}{4\pi d}\] done clear
  B)
  \[\frac{{{\mu }_{0}}I}{2\pi d}\] done clear
  C)
  \[\frac{{{\mu }_{0}}I}{\pi d}\] done clear
  D)
  \[\frac{2{{\mu }_{0}}I}{\pi d}\] done clear
  View Solution play_arrow

• question_answer41)
  A wire carries a current. Maintaining the same current it is bent first to form a circular plane coil of one turn which produces a magnetic field B at the centre of the coil. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre of the double loop, caused by the same current is       
  A)
  \[4B\] done clear
  B)
  \[B/4\]   done clear
  C)
  \[~B/2\] done clear
  D)
  \[2B\] done clear
  View Solution play_arrow

• question_answer42)
  Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance of 5m between them. If P and Q carry currents of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half-way between the wires is
  A)
  \[\frac{3{{\mu }_{0}}}{2\pi }\] done clear
  B)
  \[\frac{{{\mu }_{0}}}{\pi }\] done clear
  C)
  \[\frac{\sqrt{3}{{\mu }_{0}}}{2\pi }\] done clear
  D)
  \[\frac{{{\mu }_{0}}}{2\pi }\] done clear
  View Solution play_arrow

• question_answer43)
  Consider two thin identical conducting wires covered with very thin insulating material. One of the wires is bent into a loop and produces magnetic field\[{{B}_{1}}\], at its centre when a current I passes through it. The ratio  \[{{B}_{1}}:{{B}_{2}}\] is: 
  A)
  1 : 1  done clear
  B)
  1 : 3  done clear
  C)
  1 : 9 done clear
  D)
  9 : 1 done clear
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• question_answer44)
  Two wires are wrapped over a wooden cylinder to form two coaxial loops a carrying current\[{{i}_{1}}\] and\[{{i}_{2}}\]. If \[{{i}_{2}}=8{{i}_{1}}\] the value of x for B = 0 at the origin O is:        
  A)
  \[\sqrt{(\sqrt{7}}-1)R\]     done clear
  B)
  \[\sqrt{5}R\] done clear
  C)
  \[\sqrt{3}R\]                   done clear
  D)
  \[\sqrt{7}R\] done clear
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• question_answer45)
  Two long parallel wires carry equal current I flowing in the same direction are at a distance 2d apart. The magnetic field B at a point lying on the perpendicular line joining the wires and at a distance x from the midpoint is -
  A)
  \[\frac{{{\mu }_{0}}id}{\pi ({{d}^{2}}+{{x}^{2}})}\]            done clear
  B)
  \[\frac{{{\mu }_{0}}ix}{\pi ({{d}^{2}}-{{x}^{2}})}\] done clear
  C)
  \[\frac{{{\mu }_{0}}ix}{({{d}^{2}}+{{x}^{2}})}\]     done clear
  D)
  \[\frac{{{\mu }_{0}}id}{({{d}^{2}}+{{x}^{2}})}\] done clear
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• question_answer46)
  The current density \[\vec{j}\] inside a long, solid, cylindrical wire of radius a=12 mm is in the direction of the central axis, and its magnitude varies linearly with radial distance r from the axis according to\[J=\frac{{{J}_{0}}r}{a}\], where \[{{J}_{0}}=\frac{{{10}^{5}}}{4\pi }A/{{m}^{2}}.\] Find the magnitude of the magnetic field at in\[\mu T\]
  A)
  \[10\mu T\] done clear
  B)
  \[4\mu T\] done clear
  C)
  \[5\mu T\] done clear
  D)
  \[3\mu T\] done clear
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• question_answer47)
  A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B', at radial distances \[\frac{a}{2}\] and 2a respectively, from the axis of the wire is:
  A)
  \[\frac{1}{4}\] done clear
  B)
  \[\frac{1}{2}\]     done clear
  C)
  1 done clear
  D)
  4 done clear
  View Solution play_arrow

• question_answer48)
  An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude:
  A)
  Zero done clear
  B)
  \[\frac{{{\mu }_{0}}{{n}^{2}}e}{r}\] done clear
  C)
  \[\frac{{{\mu }_{0}}ne}{2r}\] done clear
  D)
  \[\frac{{{\mu }_{0}}ne}{2\pi r}\] done clear
  View Solution play_arrow

• question_answer49)
  A wire carrying current I has the shape as shown in adjoining figure. Linear parts of the wire are very long and parallel to X-axis while semicircular portion of radius R is lying in Y-Z plane. Magnetic field at point 0 is:             
  A)
  \[\overset{\to }{\mathop{B}}\,=-\frac{{{\mu }_{0}}}{4\pi }\frac{I}{R}\left( \mu \hat{i}\times 2\hat{k} \right)\] done clear
  B)
  \[\overset{\to }{\mathop{B}}\,=-\frac{{{\mu }_{0}}}{4\pi }\frac{I}{R}\left( \pi \hat{i}+2\hat{k} \right)\] done clear
  C)
  \[\overset{\to }{\mathop{B}}\,=\frac{{{\mu }_{0}}}{4\pi }\frac{I}{R}\left( \pi \hat{i}-2\hat{k} \right)\] done clear
  D)
  \[\overset{\to }{\mathop{B}}\,=\frac{{{\mu }_{0}}}{4\pi }\frac{I}{R}\left( \pi \hat{i}+2\hat{k} \right)\] done clear
  View Solution play_arrow

• question_answer50)
  A small current element of length \[d\ell \]and carrying current is placed at (1, 1, 0) and is carrying current in \['+z'\] direction. If magnetic field at origin be B\[{{\vec{B}}_{1}}\] and at point (2, 2, 0) be \[{{\vec{B}}_{2}}\] then:
  A)
  \[{{\vec{B}}_{1}}={{\vec{B}}_{2}}\] done clear
  B)
  \[\left. \left| {{{\vec{B}}}_{1}} \right. \right|=\left| 2\left. {{{\vec{B}}}_{2}} \right| \right.\] done clear
  C)
  \[{{\vec{B}}_{1}}=-{{\vec{B}}_{2}}\] done clear
  D)
  \[{{\vec{B}}_{1}}=-\,2{{\vec{B}}_{2}}\] done clear
  View Solution play_arrow

• question_answer51)
  In the figure shown a coil of single turn is wound on a sphere of radius R and mass M. The plane of the coil is parallel to the plane and lies in the equatorial plane of the sphere. Current in the coil is i. The value of B if the sphere is in equilibrium is        
  A)
  \[\frac{mg\,\cos \,\theta }{\pi iR}\] done clear
  B)
  \[\frac{mg\,}{\pi iR}\]     done clear
  C)
  \[\frac{mg\,\tan \,\theta }{\pi iR}\] done clear
  D)
  \[\frac{mg\,\sin \,\theta }{\pi iR}\] done clear
  View Solution play_arrow

• question_answer52)
  In the loops shown in figure, all curved sections are either semi-circles or quarter circles. All the loops carry same current. The magnetic fields at the centres have magnitudes\[{{B}_{1}}\], \[{{B}_{2}}\], \[{{B}_{3}}\], and\[{{B}_{4}}\] Then, which is correct?                           
  A)
  \[{{B}_{1}}>{{B}_{2}}>{{B}_{3}}>{{B}_{4}}\] done clear
  B)
  \[{{B}_{3}}>{{B}_{4}}>{{B}_{1}}>{{B}_{1}}\] done clear
  C)
  \[{{B}_{4}}>{{B}_{1}}>{{B}_{2}}>{{B}_{3}}\] done clear
  D)
  \[{{B}_{1}}>{{B}_{4}}>{{B}_{3}}>{{B}_{2}}\] done clear
  View Solution play_arrow

• question_answer53)
  A current loop consists of two identical semicircular parts each of radius R, one lying in the x-y plane and the other in x-z plane. If the current in the loop is i, the resultant magnetic field due to the two semicircular parts at their common centre is
  A)
  \[\frac{{{\mu }_{0}}i}{\sqrt{2}R}\] done clear
  B)
  \[\frac{{{\mu }_{0}}i}{2\sqrt{2}R}\] done clear
  C)
  \[\frac{{{\mu }_{0}}i}{2R}\] done clear
  D)
  \[\frac{{{\mu }_{0}}i}{4R}\] done clear
  View Solution play_arrow

• question_answer54)
  Five very long, straight insulated wires are closely bound together to form a small cable. Currents carried by the wires are: \[{{I}_{1}}=20\,A\], \[{{I}_{2}}=-6A\], \[{{I}_{3}}=12A\], \[{{I}_{4}}=-7A\], \[{{I}_{5}}=18A\]. (Negative currents are opposite in direction to the positive). The magnetic field induction at a distance of 10 cm from the cable is
  A)
  \[5\mu T\] done clear
  B)
  \[15\mu T\] done clear
  C)
  \[74\mu T\] done clear
  D)
  \[128\mu T\] done clear
  View Solution play_arrow

• question_answer55)
  The magnetic field at O due to current in the infinite wire forming a loop as shown in Fig. is
  A)
  \[\frac{{{\mu }_{0}}I}{2\pi d}(\cos {{\phi }_{1}}+\cos {{\phi }_{2}})\]   done clear
  B)
  \[\frac{{{\mu }_{0}}I2I}{4\pi d}(tan{{\theta }_{1}}+\tan {{\theta }_{2}})\] done clear
  C)
  \[\frac{{{\mu }_{0}}I}{4\pi d}(sin{{\phi }_{1}}+\sin {{\phi }_{2}})\] done clear
  D)
  \[\frac{{{\mu }_{0}}I}{4\pi d}(cos{{\theta }_{1}}+\sin {{\theta }_{2}})\] done clear
  View Solution play_arrow

• question_answer56)
  A current I flows through a thin wire shaped as regular polygon of n sides which can be inscribed in a circle of radius R. The magnetic field induction at the center of polygon due to one side of the polygon is  
  A)
  \[\frac{{{\mu }_{0}}I}{\pi R}\left( \tan \frac{\pi }{n} \right)\] done clear
  B)
  \[\frac{{{\mu }_{0}}I}{4\pi R}\left( \tan \frac{\pi }{n} \right)\] done clear
  C)
  \[\frac{{{\mu }_{0}}I}{2\pi R}\left( \tan \frac{\pi }{n} \right)\] done clear
  D)
  \[\frac{{{\mu }_{0}}I}{2\pi R}\left( \cos \frac{\pi }{n} \right)\] done clear
  View Solution play_arrow

• question_answer57)
  A thin rod is bent in the shape of a small circle of radius r. If the charge per unit length of the rod is a, and if the circle is rotated about its axis at a rate of n rotations per second, the magnetic induction at a point on the axis at a large distance y from the centre          
  A)
  \[{{\mu }_{0}}\pi {{r}^{3}}n\frac{\sigma }{{{y}^{3}}}\] done clear
  B)
  \[2{{\mu }_{0}}\pi {{r}^{3}}n\frac{\sigma }{{{y}^{3}}}\] done clear
  C)
  \[\left( \frac{{{\mu }_{0}}}{4\pi } \right){{r}^{3}}n\frac{\sigma }{{{y}^{3}}}\] done clear
  D)
  \[\left( \frac{{{\mu }_{0}}}{2\pi } \right){{r}^{3}}n\frac{\sigma }{{{y}^{3}}}\] done clear
  View Solution play_arrow

• question_answer58)
  Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that 'O' is their common point for the two. The wires carry\[{{I}_{1}}\]and \[{{I}_{2}}\] currents respectively. Point T' is lying at distance 'd' from 'O' along a direction perpendicular to the plane containing the wires. The magnetic field at the point 'P' will be: 
  A)
  \[\frac{{{\mu }_{0}}}{2\pi d}\left( \frac{{{I}_{1}}}{{{I}_{2}}} \right)\] done clear
  B)
  \[\frac{{{\mu }_{0}}}{2\pi d}\left( {{I}_{1}}+{{I}_{2}} \right)\] done clear
  C)
  \[\frac{{{\mu }_{0}}}{2\pi d}\left( I_{1}^{2}-I_{2}^{2} \right)\] done clear
  D)
  \[\frac{{{\mu }_{0}}}{2\pi d}{{\left( I_{1}^{2}\times I_{2}^{2} \right)}^{1/2}}\] done clear
  View Solution play_arrow

• question_answer59)
  Two similar coils of radius R are lying concentrically with their planes at right angles to each other. The currents flowing in them are I and 2I, respectively The resultant magnetic field induction at the centre will be:
  A)
  \[\frac{\sqrt{5}{{\mu }_{0}}I}{2R}\] done clear
  B)
  \[\frac{3{{\mu }_{0}}I}{2R}\] done clear
  C)
  \[\frac{{{\mu }_{0}}I}{2R}\] done clear
  D)
  \[\frac{{{\mu }_{0}}I}{R}\] done clear
  View Solution play_arrow

• question_answer60)
  The magnetic field at point 'C' due to current flowing in 'M' shape figure is
  A)
  \[\frac{{{\mu }_{0}}}{2\pi }.\frac{\sqrt{3}i}{\ell }\] done clear
  B)
  \[\frac{{{\mu }_{0}}}{\pi }.\frac{i}{\ell }\sqrt{3}\] done clear
  C)
  zero done clear
  D)
  \[\frac{{{\mu }_{0}}}{4\pi }.\frac{i}{\ell \sqrt{3}}\] done clear
  View Solution play_arrow

• question_answer61)
  A steady current is flowing in a circular coil of radius R, made up of a thin conducting wire. The magnetic field at the center of the loop is\[{{B}_{L}}\]. Now, a circular loop of radius R/n is made form the same wire without changing its length, by unfolding and refolding the loop, and the same current is passed through it. If new magnetic field at the center of the coil is \[{{B}_{C}}\], then the ratio \[{{B}_{L}}/{{B}_{C}}\] is
  A)
  \[1:{{n}^{2}}\]                        done clear
  B)
  \[{{n}^{1/2}}\] done clear
  C)
  \[n:1\]                done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer62)
  A coaxial cable consists of a thin inner conductor fixed along the axis of a hollow outer conductor. The two conductors carry equal currents in opposites directions. Let \[{{B}_{1}}\]and \[{{B}_{2}}\] be the magnetic fields in the region between the conductors and outside the conductor, respectively Then,     
  A)
  \[{{B}_{1}}\ne 0,\,{{B}_{2}}\ne 0\] done clear
  B)
  \[{{B}_{1}}={{B}_{2}}=0\] done clear
  C)
  \[{{B}_{1}}\ne 0,{{B}_{2}}=0\] done clear
  D)
  \[{{B}_{1}}=0,{{B}_{2}}\ne 0\] done clear
  View Solution play_arrow

• question_answer63)
  Two very long, straight wires carrying, currents as shown in Fig. Find all locations where the net magnetic field is zero.
  A)
  \[y=\sqrt{2}x\] done clear
  B)
  \[y=x\] done clear
  C)
  \[y=-x\] done clear
  D)
  \[y=-(x/2)\] done clear
  View Solution play_arrow

• question_answer64)
  A current I flows in the anticlockwise direction through a square loop of side a lying in the XOY plane with its center at the origin. The magnetic induction at the center of the square loop is
  A)
  \[\frac{2\sqrt{2}{{\mu }_{0}}I}{\pi a}{{\hat{e}}_{x}}\]  done clear
  B)
  \[\frac{2\sqrt{2}{{\mu }_{0}}I}{\pi a}{{\hat{e}}_{z}}\] done clear
  C)
  \[\frac{2\sqrt{2}{{\mu }_{0}}I}{\pi {{a}^{2}}}{{\hat{e}}_{z}}\]           done clear
  D)
  \[\frac{2\sqrt{2}{{\mu }_{0}}I}{\pi {{a}^{2}}}{{\hat{e}}_{x}}\] done clear
  View Solution play_arrow

• question_answer65)
  Two equal electric currents are flowing perpendicular to each other as shown in the figure. AB and CD are perpendicular to each other and symmetrically placed with respect to the current flow. Where do we expect the resultant magnetic field to be zero?     
  A)
  on AB           done clear
  B)
  on CD              done clear
  C)
  on both AB and CD       done clear
  D)
  on both OD and BO    done clear
  View Solution play_arrow

• question_answer66)
  A long straight wire of radius R carries current i. The magnetic field inside the wire at distance r from its centre is expressed as:
  A)
  \[\left( \frac{{{\mu }_{0}}i}{\pi {{R}^{2}}} \right).r\] done clear
  B)
  \[\left( \frac{2{{\mu }_{0}}i}{\pi {{R}^{2}}} \right).r\] done clear
  C)
  \[\left( \frac{{{\mu }_{0}}i}{2\pi {{R}^{2}}} \right).r\] done clear
  D)
  \[\left( \frac{{{\mu }_{0}}i}{2\pi R} \right).r\] done clear
  View Solution play_arrow

• question_answer67)
  Three infinitely long wires are placed equally apart on the circumference of a circle of radius a, perpendicular to its plane. Two of the wires carry current I each, in the same direction, while the third carries current 2I along the direction oppo- site to the other two. The magnitude of the magnetic indution \[\overset{\to }{\mathop{B}}\,\] at a distance r from the centre of the circle, for r > a, is 
  A)
  0 done clear
  B)
  \[\frac{2{{\mu }_{0}}}{\pi }\frac{I}{r}\] done clear
  C)
  \[-\frac{2{{\mu }_{0}}}{\pi }\frac{I}{r}\] done clear
  D)
  \[\frac{2{{\mu }_{0}}}{\pi }\frac{Ia}{{{r}^{2}}}\] done clear
  View Solution play_arrow

• question_answer68)
  The magnetic moment of a circular coil carrying current is
  A)
  directly proportional to the length of the wire in the coil done clear
  B)
  inversely proportional to the length of the wire in the coil done clear
  C)
  directly proportional to the square of the length of the wire in the coil done clear
  D)
  inversely proportional to the square of the length of the wire in the coil done clear
  View Solution play_arrow

• question_answer69)
  The figure shows two long straight current carrying wire separated by a fixed distance d. The magnitude of current, flowing in each wire varies with time but the magnitude of current in each wire is equal at all times. Which of the following graphs shows the correct variation of force per unit length/between the two wires with current?      
  A)
  done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
  View Solution play_arrow

• question_answer70)
  A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is \[\overset{\to }{\mathop{F}}\,\], the net force on the remaining three arms of the loop is
  A)
  \[3\overset{\to }{\mathop{F}}\,\]  done clear
  B)
  \[-\overset{\to }{\mathop{F}}\,\]  done clear
  C)
  \[-3\overset{\to }{\mathop{F}}\,\] done clear
  D)
   \[\overset{\to }{\mathop{F}}\,\] done clear
  View Solution play_arrow

• question_answer71)
  A current carrying conductor placed in a magnetic field experiences maximum force when angle between current and magnetic field is
  A)
  \[3\pi /4\] done clear
  B)
  \[\pi /2\]   done clear
  C)
  \[\pi /4\] done clear
  D)
  zero done clear
  View Solution play_arrow

• question_answer72)
  Through two parallel wires A and B, 10A and 2A of currents are passed respectively in opposite directions. If the wire A is infinitely long and the length of the wire B is 2m, then force on the conductor B, which is situated at 10 cm distance from A, will be
  A)
  \[8\times {{10}^{-7}}N\] done clear
  B)
  \[8\times {{10}^{-5}}N\] done clear
  C)
  \[4\times {{10}^{-7}}N\] done clear
  D)
  \[4\times {{10}^{-5}}N\] done clear
  View Solution play_arrow

• question_answer73)
  An 8 cm long wire carrying a current of 10 A is placed inside a solenoid perpendicular to its axis. If the magnetic field inside the solenoid is 0.3 T, then magnetic force on the wire is
  A)
  0.14N done clear
  B)
  0.24 N done clear
  C)
  0.34 N done clear
  D)
  0.44N done clear
  View Solution play_arrow

• question_answer74)
  The orbital speed of electron orbiting around a nucleus in a circular orbit of radius 50 pm is\[2.2\times {{10}^{6}}\,m{{s}^{-1}}\]. Then the magnetic dipole moment of an electron is                      
  A)
  \[1.6\times {{10}^{-19}}A{{m}^{2}}\] done clear
  B)
  \[5.3\times {{10}^{-21}}A{{m}^{2}}\] done clear
  C)
  \[8.8\times {{10}^{-26}}A{{m}^{2}}\] done clear
  D)
  \[8.8\times {{10}^{-25}}A{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer75)
  A conducting ring of mass 2kg and radius 0.5 m is placed ring on a smooth horizonatal  plane. The ring carries a current of i\[i=4A\]. A horizontal magnetic field B = 10 T is switched on at time t = 0 as shown in fig. The initial angular acceleration of the ring will be
  A)
  \[40\,\pi \,rad\,{{s}^{-2}}\] done clear
  B)
  \[20\,\pi \,rad\,{{s}^{-2}}\] done clear
  C)
  \[5\,\pi \,rad\,{{s}^{-2}}\] done clear
  D)
  \[15\,\pi \,rad\,{{s}^{-2}}\] done clear
  View Solution play_arrow

• question_answer76)
  A current carrying loop is placed in the non-uniform magnetic field whose variation in space is shown in fig. Direction of magnetic field is into the plane of paper. The magnetic force   experienced by the loop is 
  A)
  non-zero done clear
  B)
  zero                   done clear
  C)
  cannot say anything done clear
  D)
  None of the above done clear
  View Solution play_arrow

• question_answer77)
  An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current T along the same direction is shown in fig. Magnitude of force per unit a length on the middle wire 'B' is given by
  A)
  \[\frac{2{{\mu }_{0}}{{i}^{2}}}{\pi d}\] done clear
  B)
  \[\frac{\sqrt{2}{{\mu }_{0}}{{i}^{2}}}{\pi d}\] done clear
  C)
  \[\frac{{{\mu }_{0}}{{i}^{2}}}{\sqrt{2}\pi d}\] done clear
  D)
  \[\frac{{{\mu }_{0}}{{i}^{2}}}{2\pi d}\] done clear
  View Solution play_arrow

• question_answer78)
  A square loop ABCD carrying a current i, is placed near and coplanar  with a long straight      conductor XY carrying a current I, the net force on the Loop will be:          
  A)
  \[\frac{2{{\mu }_{0}}Ii}{3\pi }\] done clear
  B)
  \[\frac{{{\mu }_{0}}Ii}{2\pi }\] done clear
  C)
  \[\frac{2{{\mu }_{0}}IiL}{3\pi }\]           done clear
  D)
  \[\frac{{{\mu }_{0}}IiL}{2\pi }\] done clear
  View Solution play_arrow

• question_answer79)
  A long straight wire carries a certain current and produces a magnetic field of \[2\times {{10}^{-4}}\frac{weber}{{{m}^{2}}}\]at a perpendicular distance of 5 cm from the wire. An electron situated at 5 cm from the wire moves with a velocity \[{{10}^{7}}\,m/s\] towards the wire along perpendicular to it. The force experienced by the electron will be (charge on electron\[=1.6\times {{10}^{-19}}N\])
  A)
  Zero done clear
  B)
  \[3.2\,N\] done clear
  C)
  \[3.2\,\times {{10}^{-16}}N\] done clear
  D)
  \[1.6\,\times {{10}^{-16}}N\] done clear
  View Solution play_arrow

• question_answer80)
  A circular coil ABCD carrying a current i is placed in a uniform magnetic field. If the magnetic force on the segment AB is \[\overset{\to }{\mathop{F}}\,\]the force on the remaining segment \[BCDA\] is
  A)
  \[\overset{\to }{\mathop{F}}\,\]  done clear
  B)
  \[\overset{\to }{\mathop{-F}}\,\] done clear
  C)
  \[3\overset{\to }{\mathop{F}}\,\] done clear
  D)
  \[-3\overset{\to }{\mathop{F}}\,\] done clear
  View Solution play_arrow

• question_answer81)
  A current carrying loop in the form of a right angle isosceles triangle ABC is placed in a uniform magnetic field acting along AB. If the magnetic force on the arm BC is F, what is the force on the arm AC?
  A)
  \[-\sqrt{2}\overset{\to }{\mathop{F}}\,\] done clear
  B)
  \[-\overset{\to }{\mathop{F}}\,\] done clear
  C)
  \[\overset{\to }{\mathop{F}}\,\] done clear
  D)
  \[\sqrt{2}\overset{\to }{\mathop{F}}\,\] done clear
  View Solution play_arrow

• question_answer82)
  A closely wound solenoid of 2000 turns and area of cross-section \[1.5\times {{10}^{-4}}\,{{m}^{2}}\] carries a current of 2.0 A. It suspended through its centre and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field \[5\times {{10}^{-2}}\]tesla making an angle of \[30{}^\circ \] with the axis of the solenoid. The torque on the solenoid will be;
  A)
  \[3\times {{10}^{-2}}N-m\] done clear
  B)
  \[3\times {{10}^{-3}}N-m\] done clear
  C)
  \[1.5\times {{10}^{-3}}N-m\] done clear
  D)
  \[1.5\times {{10}^{-2}}N-m\] done clear
  View Solution play_arrow

• question_answer83)
  The figure shows two infinite semi-cylindrical shells: shell-1 and shell-2. Shell-1 carries current\[{{i}_{1}}\], in inward direction normal to the plane of paper, while shell-2 carries same current\[{{i}_{1}}\], in opposite direction. A long straight conductor lying along the common axis of the shells is carrying current\[{{i}_{2}}\]in direction same as that of current in shell-1. Force per unit length on the wire is
  A)
  zero done clear
  B)
  \[\frac{{{\mu }_{0}}{{i}_{1}}{{i}_{2}}}{2\pi r}\] done clear
  C)
  \[\frac{2{{\mu }_{0}}{{i}_{1}}{{i}_{2}}}{\pi r}\] done clear
  D)
  \[\frac{2{{\mu }_{0}}{{i}_{1}}{{i}_{2}}}{{{\pi }^{2}}r}\] done clear
  View Solution play_arrow

• question_answer84)
  A circular arc QTS is kept in an external magnetic field \[{{\overset{\to }{\mathop{B}}\,}_{0}}\] as shown in figure. The arc carries a cur- rent I. The magnetic field is directed normal and into the page. The force acting on the arc is
  A)
  \[2I{{B}_{0}}R\hat{k}\] done clear
  B)
  \[I{{B}_{0}}R\hat{k}\] done clear
  C)
  \[-2I{{B}_{0}}R\hat{k}\]            done clear
  D)
  \[-I{{B}_{0}}R\hat{k}\] done clear
  View Solution play_arrow

• question_answer85)
  The magnetic force acting on the rod ABC in the presence of external magnetic field as shown in the figure is       
  A)
  \[BI\ell \]            done clear
  B)
  \[2BI\ell \] done clear
  C)
  \[BI\ell \sqrt{3}\] done clear
  D)
  Zero done clear
  View Solution play_arrow

• question_answer86)
  Two long straight parallel wires, carrying (adjustable) current \[{{I}_{1}}\]and\[{{I}_{2}}\], are kept at a distance d apart. If the force 'F' between the two wires is taken as 'positive' when the wires repel each other and 'negative' when the wires attract each other, the graph showing the dependence of 'F' on the product\[{{I}_{1}}\,{{I}_{2}}\], would be:
  A)
  done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
  View Solution play_arrow

• question_answer87)
  A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segment PS, SR and RQ are \[{{F}_{1}}\], \[{{F}_{2}}\] and \[{{F}_{3}}\] respectively and are in the plane of the paper and along the directions shown, the force on the segment QP is       
  A)
  \[\sqrt{{{({{F}_{3}}-{{F}_{1}})}^{2}}-F_{2}^{2}}\] done clear
  B)
  \[{{F}_{3}}+{{F}_{1}}-{{F}_{2}}\] done clear
  C)
  \[{{F}_{3}}-{{F}_{1}}+{{F}_{2}}\] done clear
  D)
  \[\sqrt{{{({{F}_{3}}-{{F}_{1}})}^{2}}+F_{2}^{2}}\] done clear
  View Solution play_arrow

• question_answer88)
  A conducting wire bent in the form of a parabola\[{{y}^{2}}=2x\]carries a current \[i=2A\]as shown in figure. This wire is placed in a uniform magnetic field \[\overset{\to }{\mathop{B}}\,=-4\hat{k}\]tesla. The magnetic force on the wire (in newton)
  A)
  \[-16\hat{i}\] done clear
  B)
  \[32\hat{i}\]    done clear
  C)
  \[-32\hat{i}\] done clear
  D)
  \[16\hat{i}\] done clear
  View Solution play_arrow

• question_answer89)
  A conducting loop is placed in a magnetic field of strength B perpendicular to its plane. Radius of the loop is r, current in the loop is; and linear mass density of the wire of loop is m. Speed of any transverse wave in the loop will be
  A)
  \[\sqrt{\frac{Bir}{m}}\] done clear
  B)
  \[\sqrt{\frac{Bir}{2m}}\] done clear
  C)
  \[\sqrt{\frac{2Bir}{m}}\] done clear
  D)
  \[2\sqrt{\frac{Bir}{m}}\] done clear
  View Solution play_arrow

• question_answer90)
  A wire carrying current I is tied between points P and Q and is in the shape of a circular arc of radius R due to a uniform magnetic field B    (perpendicular to the plane of the paper, shown by xxx) in the vicinity of the wire. If the wire subtends an angle \[2{{\theta }_{0}}\] at the centre of the circle (of which it forms an arc) then the tension in the wire is:
  A)
  \[\frac{IBR}{2\,\sin \,{{\theta }_{0}}}\] done clear
  B)
  \[\frac{IBR{{\theta }_{0}}}{\sin \,{{\theta }_{0}}}\] done clear
  C)
  \[IBR\] done clear
  D)
  \[\frac{IBR}{\sin {{\theta }_{0}}}\] done clear
  View Solution play_arrow

• question_answer91)
  A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10-divisions per milliamp ere and voltage sensitivity is 2 divisions per millivolt. In order that each division reads 1 volt, the resistance in ohms needed to be connected in series with the coil will be
  A)
  \[{{10}^{5}}\]  done clear
  B)
  \[{{10}^{3}}\]   done clear
  C)
  9995 done clear
  D)
  99995 done clear
  View Solution play_arrow

• question_answer92)
  A \[50\Omega \] resistance is connected to a battery of 5V. A galvanometer of resistance\[100\Omega \] is to be used as an ammeter to measure current through the resistance, for this a resistance\[{{r}_{s}}\]is connected to the galvanometer. Which of the following connections should be employed if the measured current is within 1% of the current without the ammeter in the circuit?     
  A)
  \[{{r}_{s}}=0.5\Omega \] in series with the galvanometer done clear
  B)
  \[{{r}_{s}}=1\Omega \] in series with galvanometer done clear
  C)
  \[{{r}_{s}}=1\Omega \] in parallel with galvanometer done clear
  D)
  \[{{r}_{s}}=0.5\Omega \] in parallel with the galvanometer done clear
  View Solution play_arrow

• question_answer93)
  A galvanometer of resistance 50 Q is connected to battery of 3V along with a resistance of 2950 Q in series. A full scale deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to 20 divisions, the resistance in series should be
  A)
  \[5050\Omega \] done clear
  B)
  \[5550\Omega \] done clear
  C)
  \[6050\Omega \] done clear
  D)
  \[4450\Omega \] done clear
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• question_answer94)
  A circuit contains an ammeter, a battery of 30V and a resistance\[40.8\Omega \] all connected in series. If the ammeter has a coil of resistance \[480\Omega \] and a shunt of 200, the reading in the ammeter will be:
  A)
  0.25 A done clear
  B)
  2 A   done clear
  C)
  1 A  done clear
  D)
  0.5 A done clear
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• question_answer95)
  In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is Q the resistance of ammeter will be:
  A)
  \[\frac{1}{499}G\] done clear
  B)
  \[\frac{499}{500}G\] done clear
  C)
  \[\frac{1}{500}G\] done clear
  D)
  \[\frac{500}{499}G\] done clear
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• question_answer96)
  A voltmeter has a range 0-V with a series resistance R. With a series resistance 2R, the range is\[0-V'\]. The correct relation between V and V? is          
  A)
  \[V'=2V\] done clear
  B)
  \[V'>2V\] done clear
  C)
  \[V'>>2V\] done clear
  D)
  \[V'<2V\] done clear
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• question_answer97)
  A micrometer has a resistance of\[100\Omega \] and full scale range of\[50\mu A\]. It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resistance combination 
  A)
  50 V range with\[10k\Omega \] resistance in series done clear
  B)
  10 V range with\[200k\Omega \] resistance in series done clear
  C)
  10 mA range with\[1\Omega \] resistance in parallel done clear
  D)
  10 mA range with \[0.1\Omega \] resistance in parallel done clear
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• question_answer98)
  A milli voltmeter of 25 milli volt range is to be converted into an ammeter of 25 ampere range. The value (in ohm) of necessary shunt will be
  A)
  0.001    done clear
  B)
  0.01   done clear
  C)
  1          done clear
  D)
  0.05 done clear
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• question_answer99)
  A galvanometer of resistance 5 ohms gives a full scale deflection for a potential difference of 10 mV. To convert the galvanometer into a voltmeter giving a full scale deflection for a potential difference of IV, the size of the resistance that must be attached to the voltmeter is
  A)
  0.495 ohm done clear
  B)
  49.5 dim done clear
  C)
  495 ohm done clear
  D)
  4950 ohm done clear
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• question_answer100)
  A moving coil galvanometer has a resistance of\[900\Omega \]. In order to send only 10% of the main current through this galvanometer, the resistance of the required shunt is
  A)
  \[0.9\Omega \] done clear
  B)
  \[100\Omega \] done clear
  C)
  \[405\Omega \] done clear
  D)
  \[90\Omega \] done clear
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