Verified Solution • 2025–26 Session moderate

QJEEM20Ph0787: JEE Main 2020 Physics - Class 12 JEEM20Ph0787 Solution: A circular coil has moment of inertia 0.8 kg m 2 around any…

A circular coil has moment of inertia 0.8 kg m2 around any diameter and is carrying current to produce a magnetic moment of 20 Am2 . The coil is kept initially in a vertical position and it can rotate freely around a horizontal diameter. When a uniform magnetic field of 4 T is applied along the vertical,it starts rotating around its horizontal diameter. The angular speed the coil acquires after rotating by 60o will be:

Multiple Choice Options

  • A 10 π rad s–1
  • B 20 π rad s–1
  • C 10(3)1/4 rad s–1
  • D 20 rad s–1

Step-by-Step Verified Solution

By energy conservation

Ui + Ki = Uf + Kf

⇒ −MBcos⁡90∘+0=−MBcos⁡30∘+12Iω2

⇒ MB32 =12Iω2

⇒ ω=MB3I

= 20×4×30.8 = 103=10(3)1/4

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