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Charge Q is uniformly distributed on the...

Charge `Q` is uniformly distributed on the rim of a thin insulating disc of mass `m` which is initially at rest and placed on a smooth horizontal surface. What will be the angular velocity of the disc if a magnetic field `B`, perpendicular to the plane of the disc is switched on ?

A

`QB//2m`

B

`QB//3m`

C

`2QB//3m`

D

`QB//m`

Text Solution

Verified by Experts

`DeltaQ` on a small element `=Q(Deltal)/(2pir)`
Torque on the disc `=(Q)/(2pi)ointE_(t)Deltal`
`omega=alphaDeltat=(Q)/(2pi)(-pir^(2)(DeltaB)/(Deltat))(2)/(mr^(2))Deltat=(2Q)/(2m)DeltaB=(QB)/(m)` (initially `B` was zero)
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