Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Magnetism and Matter question

2012 · Q91
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /NEET
  3. /Physics
  4. /Magnetism and Matter
  5. /2012 · Q91

Magnetism and Matter question

2012 · Q91

NEETPhysicsMagnetism and MatterMCQ+4 / −1
A magnetic needle suspended parallel to a magnetic field requires 3J\sqrt 3 J3​J of work to turn it through 60o. The torque needed to maintain the needle in this position will be
  1. A
    23J2\sqrt 3 J23​J
  2. B
    333 JJJ
  3. C
    3 J\sqrt 3 \,J3​J
  4. D
    32 J{3 \over 2}\,J23​J
View written solutionFree

Correct answer: B

According to work energy theorem

W = Ufinal – Uinitial = MB (cos 0 – cos 60°) = MB2{{MB} \over 2}2MB​ = 3J\sqrt 3 J3​J ....(1)

The torque on the needle is

τ→=M→×B→=MBsin⁡θ\overrightarrow \tau = \overrightarrow M \times \overrightarrow B = MB\sin \theta τ=M×B=MBsinθ

= MBsin⁡60∘MB\sin 60^\circ MBsin60∘ = MB32{{MB\sqrt 3 } \over 2}2MB3​​ ....(2)

From equation (1) and (2),

τ\tau τ = 23×32{{2\sqrt 3 \times \sqrt 3 } \over 2}223​×3​​ = 3 J

PreviousNext

More from Magnetism and Matter

  • A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It2012 · MCQ
  • A short bar magnet of magnetic moment 0.4 J T−1 is placed in a uniform magnetic field of 0.16 T. The magnet is in stable equilibrium when the potential energy is2011 · MCQ
  • There are four light-weight-rod samples A, B, C, D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted (i) A is feebly repelled (ii) B is feebly attracted (iii) C is…2011 · MCQ
  • The magnetic moment of a diamagnetic action is2010 · MCQ
  • Two identical bar magnets are fixed with their centers at a distance d apart. A stationary charge Q is placed at P in between the gap of the two magnets at a distance D from the centre O as shown in the figure The force on the charge Q is Includes diagram2010 · MCQ
  • Electromagnets are made of soft iron because soft iron has2010 · MCQ
  • A vibration magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with a time period of 2 sec in earth's horizontal magnetic field of 24 microtesla. When a horizontal field of 18 microtesla is…2010 · MCQ
  • If a diamagnetic substance is brought near the north or the south pole of a bar magnet, it is2009 · MCQ