JEE Main & Advanced Physics Magnetism Question Bank

done Critical Thinking Total Questions - 25

• question_answer1)
  Two identical magnetic dipoles of magnetic moments 1.0 A-m2 each, placed at a separation of 2m with their axis perpendicular to each other. The resultant magnetic field at a point midway between the dipoles is        [Roorkee 1995]
  A)
             \[5\times {{10}^{-7}}T\]   done clear
  B)
             \[\sqrt{5}\times {{10}^{-7}}T\] done clear
  C)
             \[{{10}^{-7}}T\]                    done clear
  D)
             None of these done clear
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• question_answer2)
  Two short magnets placed along the same axis with their like poles facing each other repel each other with a force which varies inversely as
  A)
             Square of the distance done clear
  B)
             Cube of the distance done clear
  C)
             Distance done clear
  D)
             Fourth power of the distance done clear
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• question_answer3)
  Two identical short bar magnets, each having magnetic moment M, are placed a distance of 2d apart with axes perpendicular to each other in a horizontal plane. The magnetic induction at a point midway between them is [IIT-JEE (Screening) 2000]
  A)
             \[\frac{{{\mu }_{0}}}{4\pi }(\sqrt{2})\frac{M}{{{d}^{3}}}\]  done clear
  B)
             \[\frac{{{\mu }_{0}}}{4\pi }(\sqrt{3})\frac{M}{{{d}^{3}}}\]  done clear
  C)
             \[\left( \frac{2{{\mu }_{0}}}{\pi } \right)\,\frac{M}{{{d}^{3}}}\]        done clear
  D)
             \[\frac{{{\mu }_{0}}}{4\pi }(\sqrt{5})\frac{M}{{{d}^{3}}}\] done clear
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• question_answer4)
  If a magnet is suspended at an angle 30o to the magnetic meridian, it makes an angle of 45o with the horizontal. The real dip is  
  A)
             \[{{\tan }^{-1}}(\sqrt{3}/2)\]  done clear
  B)
             \[{{\tan }^{-1}}(\sqrt{3)}\] done clear
  C)
             \[{{\tan }^{-1}}(\sqrt{3/2})\]  done clear
  D)
             \[{{\tan }^{-1}}(2/\sqrt{3})\] done clear
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• question_answer5)
  A short bar magnet with its north pole facing north forms a neutral point at P in the horizontal plane. If the magnet is rotated by 90o in the horizontal plane, the net magnetic induction at P is (Horizontal component of earth?s magnetic field = \[{{B}_{H}}\])                                     [EAMCET (Engg.) 2000]
  A)
             0     done clear
  B)
             2 BH  done clear
  C)
             \[\frac{\sqrt{5}}{2}{{B}_{H}}\]                                           done clear
  D)
             \[\sqrt{5}\,{{B}_{H}}\] done clear
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• question_answer6)
  The true value of angle of dip at a place is 60o, the apparent dip in a plane inclined at an angle of 30o with magnetic meridian is                                                                        [AIEEE 2002]
  A)
             \[{{\tan }^{-1}}\frac{1}{2}\]    done clear
  B)
             \[{{\tan }^{-1}}(2)\]   done clear
  C)
             \[{{\tan }^{-1}}\left( \frac{2}{3} \right)\]                      done clear
  D)
             None of these done clear
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• question_answer7)
  A vibration magnetometer consists of two identical bar magnets placed one over the other such that they are perpendicular and bisect each other. The time period of oscillation in a horizontal magnetic field is \[{{2}^{5/4}}\]seconds. One of the magnets is removed and if the other magnet oscillates in the same field, then the time period in seconds is                                                                              [EAMCET (Med.) 2003]
  A)
             \[{{2}^{1/4}}\]                      done clear
  B)
             \[{{2}^{1/2}}\]  done clear
  C)
             2     done clear
  D)
             \[{{2}^{3/4}}\] done clear
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• question_answer8)
  In a vibration magnetometer, the time period of a bar magnet oscillating in horizontal component of earth's magnetic field is 2 sec. When a magnet is brought near and parallel to it, the time period reduces to 1 sec. The ratio H/F of the horizontal component H and the field F due to magnet will be    [MP PMT 1990; Pb PET 2000]
  A)
             \[3\]                                         done clear
  B)
             \[1/3\] done clear
  C)
             \[\sqrt{3}\]                            done clear
  D)
             \[1/\sqrt{3}\] done clear
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• question_answer9)
  A cylindrical rod magnet has a length of 5 cm and a diameter of 1 cm. It has a uniform magnetisation of 5.30 × 103Amp/m3. What its magnetic dipole moment
  A)
             \[1\times {{10}^{-2}}J/T\]       done clear
  B)
             \[2.08\times {{10}^{-2}}J/T\] done clear
  C)
             \[3.08\times {{10}^{-2}}J/T\] done clear
  D)
              \[1.52\times {{10}^{-2}}J/T\] done clear
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• question_answer10)
  Two magnets of equal mass are joined at right angles to each other as shown the magnet 1 has a magnetic moment 3 times that of magnet 2. This arrangement is pivoted so that it is free to rotate in the horizontal plane. In equilibrium what angle will the magnet 1 subtend with the magnetic meridian
  A)
             \[{{\tan }^{-1}}\left( \frac{1}{2} \right)\] done clear
  B)
             \[{{\tan }^{-1}}\left( \frac{1}{3} \right)\] done clear
  C)
             \[{{\tan }^{-1}}(1)\] done clear
  D)
              0° done clear
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• question_answer11)
  The dipole moment of each molecule of a paramagnetic gas is 1.5 ´ 10?23 amp ´ m2. The temperature of gas is 27oC and the number of molecules per unit volume in it is 2 ´ 1026 m?3. The maximum possible intensity of magnetisation in the gas will be
  A)
             3 ´ 103 amp/m                     done clear
  B)
             4 ´ 10?3 amp/m done clear
  C)
             5 ´ 105 amp/m                     done clear
  D)
             6 ´ 10?4 amp/m done clear
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• question_answer12)
  Two magnets A and B are identical and these are arranged as shown in the figure. Their length is negligible in comparison to the separation between them. A magnetic needle is placed between the magnets at point P which gets deflected through an angle \[\theta \] under the influence of magnets. The ratio of distance \[{{d}_{1}}\] and \[{{d}_{2}}\] will be
  A)
             \[{{(2\tan \theta )}^{1/3}}\]   done clear
  B)
             \[{{(2\tan \theta )}^{-1/3}}\] done clear
  C)
             \[{{(2\cot \theta )}^{1/3}}\] done clear
  D)
             \[{{(2\cot \theta )}^{-1/3}}\] done clear
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• question_answer13)
  Two short magnets of equal dipole moments M are fastened perpendicularly at their centre (figure). The magnitude of the magnetic field at a distance d from the centre on the bisector of the right angle is
  A)
             \[\frac{{{\mu }_{0}}}{4\pi }\frac{M}{{{d}^{3}}}\] done clear
  B)
             \[\frac{{{\mu }_{0}}}{4\pi }\frac{M\sqrt{2}}{{{d}^{3}}}\] done clear
  C)
             \[\frac{{{\mu }_{0}}}{4\pi }\frac{2\sqrt{2}M}{{{d}^{3}}}\] done clear
  D)
              \[\frac{{{\mu }_{0}}}{4\pi }\frac{2M}{{{d}^{3}}}\] done clear
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• question_answer14)
  A small coil C with N = 200 turns is mounted on one end of a balance beam and introduced between the poles of an electromagnet as shown in figure. The cross sectional area of coil is A= 1.0 cm2, length of arm OA of the balance beam is \[l=30\,cm.\] When there is no current in the coil the balance is in equilibrium. On passing a current I = 22 mA through the coil the equilibrium is restored by putting the additional counter weight of mass \[\Delta m=60\,mg\] on the balance pan. Find the magnetic induction at the spot where coil is located.
  A)
             0.4 T                                          done clear
  B)
             0.3 T done clear
  C)
             0.2 T                                          done clear
  D)
             0.1 T done clear
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• question_answer15)
  Two identical bar magnets with a length 10 cm and weight 50 gm-weight are arranged freely with their like poles facing in a inverted vertical glass tube. The upper magnet hangs in the air above the lower one so that the distance between the nearest pole of the magnet is 3mm. Pole strength of the poles of each magnet will be
  A)
             6.64 amp ´ m done clear
  B)
             2 amp ´ m done clear
  C)
             10.25 amp ´ m done clear
  D)
             None of these done clear
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• question_answer16)
  If \[{{\varphi }_{1}}\] and \[{{\varphi }_{2}}\] be the angles of dip observed in two vertical planes at right angles to each other and f be the true angle of dip, then
  A)
             \[{{\cos }^{2}}\varphi ={{\cos }^{2}}{{\varphi }_{1}}+{{\cos }^{2}}{{\varphi }_{2}}\] done clear
  B)
             \[{{\sec }^{2}}\varphi ={{\sec }^{2}}{{\varphi }_{1}}+{{\sec }^{2}}{{\varphi }_{2}}\] done clear
  C)
             \[{{\tan }^{2}}\varphi ={{\tan }^{2}}{{\varphi }_{1}}+{{\tan }^{2}}{{\varphi }_{2}}\] done clear
  D)
             \[{{\cot }^{2}}\varphi ={{\cot }^{2}}{{\varphi }_{1}}+{{\cot }^{2}}{{\varphi }_{2}}\] done clear
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• question_answer17)
  Each atom of an iron bar \[(5\,cm\times 1\,cm\times 1\,cm)\] has a magnetic moment \[1.8\times {{10}^{-23}}\,A{{m}^{2}}.\] Knowing that the density of iron is \[7.78\times {{10}^{3}}\,k{{g}^{-3}}m,\] atomic weight is 56 and Avogadro's  number is \[6.02\times {{10}^{23}}\] the magnetic moment of bar in the state of magnetic saturation will be
  A)
             \[4.75\,\,A{{m}^{2}}\]       done clear
  B)
             \[5.74\,\,A{{m}^{2}}\] done clear
  C)
             \[7.54\,\,A{{m}^{2}}\]       done clear
  D)
             \[75.4\,\,A{{m}^{2}}\] done clear
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• question_answer18)
  An iron rod of volume \[{{10}^{-4}}{{m}^{3}}\] and relative permeability 1000 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 of the rod is
  A)
             \[10\,\,A{{m}^{2}}\]          done clear
  B)
             \[15\,\,A{{m}^{2}}\] done clear
  C)
             \[20\,\,A{{m}^{2}}\]          done clear
  D)
             \[25\,\,A{{m}^{2}}\] done clear
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• question_answer19)
  A bar magnet has coercivity \[4\times {{10}^{3}}\,A{{m}^{-1}}.\] It is desired to demagnetise it by inserting it inside a solenoid 12 cm long and having 60 turns. The current that should be sent through the solenoid is
  A)
             2 A done clear
  B)
             4 A done clear
  C)
             6 A done clear
  D)
             8 A done clear
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• question_answer20)
  A magnet is suspended in the magnetic meridian with an untwisted wire. The upper end of wire is rotated through 180o to deflect the magnet by 30o from magnetic meridian. When this magnet is replaced by another magnet, the upper end of wire is rotated through 270o to deflect the magnet 30o from magnetic meridian. The ratio of magnetic moments of magnets is
  A)
             1 : 5                                           done clear
  B)
             1 : 8 done clear
  C)
             5 : 8                                           done clear
  D)
             8 : 5 done clear
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• question_answer21)
  A dip needle vibrates in the vertical plane perpendicular to the magnetic meridian. The time period of vibration is found to be 2 seconds. The same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be 2 seconds. Then the angle of dip is
  A)
             0o    done clear
  B)
             30o done clear
  C)
             45o done clear
  D)
             90o done clear
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• question_answer22)
  The unit for molar susceptibility is
  A)
             m3 done clear
  B)
             kg-m?3  done clear
  C)
             kg?1 m3                                    done clear
  D)
             No units done clear
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• question_answer23)
  A short magnet oscillates with a time period 0.1 s at a place where horizontal magnetic field is \[24\mu T.\] A downward current of 18 A is established in a vertical wire 20 cm east of the magnet. The new time period of oscillator
  A)
             0.1 s                                          done clear
  B)
             0.089 s done clear
  C)
             0.076 s                                     done clear
  D)
             0.057 s done clear
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• question_answer24)
  A dip needle lies initially in the magnetic meridian when it shows an angle of dip q 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_answer25)
  A dip circle is adjusted so that its needle moves freely in the magnetic meridian. In this position, the angle of dip is 40°. Now the dip circle is rotated so that the plane in which the needle moves makes an angle of 30° with the magnetic meridian. In this position the needle will dip by an angle [DCE 2005]
  A)
             40° done clear
  B)
             30° done clear
  C)
             More than 40°                      done clear
  D)
             Less than 40° done clear
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