Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main 20204 SeptemberMorning Shift
Exam
JEE Main
Year
2020
Date
4 September
Shift
Morning Shift
Subject
Physics
Chapter
Magnetic Properties of Matter

JEE Main 2020 · 4 September · Morning Shift · Physics · Magnetic Properties of Matter

A small bar magnet is placed with its axis at 30 ^ o with an...

A small bar magnet is placed with its axis at 30o{30}^{o} with an external magnetic field of 0.06T0 . 06T experiences a torque of 0.018Nm0 . 018Nm. The minimum work required to rotate it from its stable to unstable equilibrium position is:

Options

  1. A6.4×10−2J6 . 4 \times {10}^{- 2}\text{J}
  2. B9.2×10−3J9 . 2 \times {10}^{- 3}\text{J}
  3. C7.2×10−2J7 . 2 \times {10}^{- 2}\text{J}
  4. D11.7×10−3J11 . 7 \times {10}^{- 3}\text{J}

Correct answer

C. 7.2×10−2J7 . 2 \times {10}^{- 2}\text{J}

Step-by-step solution

τ=MBsinθ=0.018τ = MBsin \theta = 0 . 018

M=0.018Bsinθ=0.0180.06×0.5=0.64Am2M = \dfrac{0 .018}{Bsin\theta} = \dfrac{0 .018}{0 .06 \times 0 .5} = 0 .64 A{m}^{2}

W=ΔU=Uf−UiW = \Delta U = {U}_{f} - {U}_{i}

=−MBcos180∘−(−MBcos0∘)= - MBcos{180}^{∘} - \left(- MBcos{0}^{∘}\right)

=2MB= 2MB

=2×0.6×0.06= 2 \times 0 .6 \times 0 .06

=0.072J= 0 . 072J

Practice Magnetic Properties of Matter on Quantrex Academy →

More from Magnetic Properties of Matter

A solenoid has a core made of material with relative permeability 400 . The magnetic… JEE Main 2026Two identical small bar magnets each of dipole moment 3 5 J/T are placed at a center to… JEE Main 2026Given below are two statements: one is labelled as Assertion (A) and the other is… JEE Main 2026Given below are two statements : one is labelled as Assertion (A) and the other is… JEE Main 2025The percentage increase in magnetic field (B) when space within a current carrying… JEE Main 2025A solenoid having area A and length ' l ' is filled with a material having relative… JEE Main 2025The relationship between the magnetic susceptibility (χ) and the magnetic permeability… JEE Main 2025A bar magnet has total length 2 l=20 units and the field point P is at a distance d=10… JEE Main 2025 Full Magnetic Properties of Matter list All JEE Main PYQs