12th Class Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank

done MCQs - Magnetism and Matter Total Questions - 14

• question_answer1)
  A toroid of n turns, mean radius R and cross- sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment m
  A)
  is non-zero and points in the z-direction by symmetry. done clear
  B)
  points along the axis of the toroid \[(m={{m}_{\phi }})\] done clear
  C)
  is zero, otherwise there would be a field falling as \[\frac{1}{{{r}^{3}}}\] at large distances outside the toroid. done clear
  D)
  is pointing radially outwards. done clear
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• question_answer2)
  Consider the two idealized systems: (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length L, R, radius of cross-section. In (i), E is ideally treated as a constant between plates and zero outside, In (ii), magnetic field is constant inside the solenoid and zero outside. These idealized assumptions, however, contradict fundamental laws as below :
  A)
  Case (i) contradicts Gauss's law for electrostatic fields. done clear
  B)
  Case (ii) contradicts Gauss's law for magnetic fields. done clear
  C)
  Case (i) agrees with \[\oint{_{s}E.dl=0}\] done clear
  D)
  Case (ii) contradicts \[\oint{H.dl={{I}_{en}}}\] done clear
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• question_answer3)
  A rod of length L, along east-west direction is dropped from a height H. If B be the magnetic field due to Earth at that place and angle of dip is 6, then the magnitude of the induced e.m.f. across two ends of the rod when the rod reachs the Earth is
  A)
  BLH cos\[\theta \] done clear
  B)
  \[BL\text{ }cos\theta \times {{(2gH)}^{1/2}}\] done clear
  C)
  \[BL\text{ }cos\theta /{{(2gH)}^{1/2}}\] done clear
  D)
  None of the above done clear
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• question_answer4)
  A coil of N turns and radius R carries a current I. It is unwound and rewound to make a square coil of side a having same number of turns (N). Keeping the current I same, the ratio of the magnetic moments of the circular coil and the square coil is
  A)
  \[\pi \frac{{{\operatorname{R}}^{2}}}{{{a}^{2}}}\] done clear
  B)
  \[\pi \frac{{{a}^{2}}}{{{\operatorname{R}}^{2}}}\] done clear
  C)
  \[\frac{{{a}^{2}}}{{{\operatorname{R}}^{2}}}\] done clear
  D)
  None of the above done clear
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• question_answer5)
  A magnetic dipole moment is a vector quantity directed from:
  A)
  South to North done clear
  B)
  North to South done clear
  C)
  East to West done clear
  D)
  West to East done clear
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• question_answer6)
  Time period of oscillation of a magnetic needle is
  A)
  \[\operatorname{T}=\sqrt{\frac{I}{MB}}\] done clear
  B)
  \[\operatorname{T}=2\pi \sqrt{\frac{\operatorname{I}}{MB}}\] done clear
  C)
  \[\operatorname{T}=2\pi \sqrt{\frac{MB}{\operatorname{I}}}\] done clear
  D)
  \[\operatorname{T}=\pi \sqrt{\frac{MB}{\operatorname{I}}}\] done clear
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• question_answer7)
  A magnetic needle is kept in a non-uniform magnetic field experiences
  A)
  a force as well as a torque done clear
  B)
  a torque but not a force done clear
  C)
  a force and a torque done clear
  D)
  a force but not a torque done clear
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• question_answer8)
  The magnetic field of Earth can be modelled by that of a point dipole placed at the centre of the Earth. The dipole axis makes an angle of \[{{11.3}^{\operatorname{o}}}\] with the axis of Earth. At Mumbai, declination is nearly zero. Then,
  A)
  the declination varies between \[{{11.3}^{\operatorname{o}}}\] W to \[{{11.3}^{\operatorname{o}}}\] E. done clear
  B)
  the least declination is \[{{0}^{\operatorname{o}}}\]. done clear
  C)
  the plane defined by dipole axis and Earth axis passes through Greenwich. done clear
  D)
  declination averaged over Earth must be always negative. done clear
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• question_answer9)
  Let the magnetic field on Earth be modelled by that of a point magnetic dipole at the centre of Earth. The angle of dip at a point on the geographical Equator
  A)
  is always zero. done clear
  B)
  is always positive done clear
  C)
  is always negative done clear
  D)
  can be positive or negative or zero. done clear
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• question_answer10)
  Relative permeability of a magnetic material is 0.5. The material is
  A)
  diamagnetic. done clear
  B)
  ferromagnetic.                                                           done clear
  C)
  paramagnetic. done clear
  D)
  not a magnetic material. done clear
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• question_answer11)
  Which of the following relation is correct?
  A)
  \[\operatorname{B}={{B}_{v}}\times {{B}_{H}}\] done clear
  B)
  \[\operatorname{B}={{B}_{v}}/{{B}_{H}}\] done clear
  C)
  \[\operatorname{B}={{B}_{v}}+{{B}_{H}}\] done clear
  D)
  \[\operatorname{B}=\sqrt{\operatorname{B}_{\operatorname{V}}^{2}+B_{H}^{2}}\] done clear
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• question_answer12)
  Ratio of total intensity of magnetic field at equator to poles is
  A)
  1:1 done clear
  B)
  1:2 done clear
  C)
  2:1 done clear
  D)
  None of the above done clear
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• question_answer13)
  Which of the following is most suitable for the core of an electromagnet?
  A)
  Soft iron done clear
  B)
  Steel done clear
  C)
  Alnico done clear
  D)
  Copper done clear
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• question_answer14)
  A ferromagnetic substance is heated above its curie temperature. Which of the following statements is correct?
  A)
  Ferromagnetic domains get perfectly arranged. done clear
  B)
  Ferromagnetic domains get randomly arranged. done clear
  C)
  Ferromagnetic domains are not at all influenced. done clear
  D)
  Ferromagnetic material transforms into diamagnetic substance. done clear
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