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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Physics
Chapter
Magnetic Properties of Matter

NTA Abhyas 2020 · Physics · Magnetic Properties of Matter

A deflection magnetometer is placed with its arm along the...

A deflection magnetometer is placed with its arm along the east-west direction (tanAposition)andashortbarmagnetisplacedsymmetricallyalongitsaxisatsomedistancewithitsnorthpolepointingtowardseast.Inthispositiontheneedleofthemagnetometershowsadeflectionof60°position) and a short bar magnet is placed symmetrically along its axis at some distance with its north pole pointing towards east. In this position the needle of the magnetometer shows a deflection of 60 °. If we double the distance of the bar magnet,& then the deflection will be

Options

  1. Asin⁡−1[38]\sin^{- 1} \left[\dfrac{\sqrt{3}}{8}\right]
  2. Bcos⁡−1[38]\cos^{- 1} \left[\dfrac{\sqrt{3}}{8}\right]
  3. Ctan⁡−1[38]\tan^{- 1} \left[\dfrac{\sqrt{3}}{8}\right]
  4. Dcot⁡−1[38]\cot^{- 1} \left[\dfrac{\sqrt{3}}{8}\right]

Correct answer

C. tan⁡−1[38]\tan^{- 1} \left[\dfrac{\sqrt{3}}{8}\right]

Step-by-step solution

For a short bar magnet in tan A& position,

μ04π2Md3=Htanθ\dfrac{\mu0}{4\pi}\dfrac{2M}{d3} = Htan \theta...(i)

When distance is doubled, then new deflection θ′\theta′ is given by,

μ04π2M(2d)3=Htanθ′\dfrac{\mu0}{4\pi}\dfrac{2M}{\left(2d\right)3} = H{tanθ}^{'} ....(ii)

∴tanθ′tanθ=18∴ \dfrac{tan {θ}^{′}}{tan \theta} = \dfrac{1}{8}

⇒tanθ′=tanθ8=tan⁡60°8=38⇒ {tan\theta}^{′} = \dfrac{tan\theta}{8} = \dfrac{\tan 60 °}{8} = \dfrac{\sqrt{3}}{8}

⇒⇒{\theta}^{′} = \tan^{- 1}$ \left[\dfrac{\sqrt{3}}{8}\right]
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