Home
Class 12
PHYSICS
A bar magnet is hung by a thin cotton th...

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by `60^(@)` is `W`. Now the torque required to keep the magnet in this new position is

A

`(W)/(sqrt3)`

B

`sqrt3W`

C

`(sqrt3W)/(2)`

D

`(2W)/(sqrt3)`

Text Solution

Verified by Experts

The correct Answer is:
B

Work done in rotating the magnet
`" " W=MB(cos theta_(0)-cos theta)`
where, M =magnetic moment of the magnet and
`" " "B=magnetic field"`
`W=MB(cos 0^(@)-cos60^(@))=MB(1-(1)/(2)) Rightarrow (MB)/(2)`
`therefore MB=2W`
Torque on a magnet in this position is given by, `tau =MxxB=MB.sin theta=2W.sin60 " " "["From Eq. (i)"]" `
`=2W (sqrt3)/(2)=Wsqrt3`
Doubtnut Promotions Banner Mobile Dark
|

Topper's Solved these Questions

  • MAGNETISM AND MATTER

    DC PANDEY|Exercise 5.3|15 Videos
  • MAGNETICS

    DC PANDEY|Exercise MCQ_TYPE|1 Videos
  • MODERN PHYSICS

    DC PANDEY|Exercise Integer Type Questions|17 Videos

Similar Questions

Explore conceptually related problems

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in' equilibrium state. The energy required to rotute it by 60^(circ) is W . Now the torque required to keep the magnet in this new: position is sqrt(k) W . Find k .

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in' equilibrium state. The energy required to rotute it by 60^(circ) is W . Now the torque required to keep the magnet in this new: position is sqrt(k) W . Find k .

Knowledge Check

  • A magnetic needle is placed in a uniform magnetic field and is aligned with the field. The needle is now rotated by an angle of 60^(@) and the work done is W. The torque on the magnetic needle at this position is

    A
    `2sqrt3W`
    B
    `sqrt3W`
    C
    `(sqrt3)/2W`
    D
    `(sqrt3)/4W`
  • A magnetic needle lying parallel to a magnetic field requires W units of work to turn through 60^(@) . The external torque required to maintain the magnetic needle in this position is

    A
    W
    B
    2 W
    C
    `(sqrt3)/(2) W`
    D
    `sqrt3` W
  • A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60^@ . The torque required to maintain the needle in this position will be

    A
    `sqrt3 ` W
    B
    W
    C
    `(sqrt3)/(2) W`
    D
    `2W`
  • Similar Questions

    Explore conceptually related problems

    A bar magnet hung by a insulating thread In a uniform horizontal magnetic field and magnet is in equilibrium Initially. The torque required to keep the magnet at angle by 30° with the direction of magnetic field is t. Then the work done to rotate it by same angle from initial position is

    A bar magnet of magnetic moment M is hung by a thin cotton thread in a uniform magnetic field B. Work done by the external agent to rotate the bar magnet from stable equilibrium position to 120° with the direction of magnetic field is (consider change in angular speed is zero)

    A magnetic needle is placed in a uniform magnetic field and is aligned with the field. The needle is now rotated by an angle of 60% and the work done is W. The torgue on the magnetic needle at this position is:

    A magnetic needle lying parallel to a magnetic field requires W units of work to tum it through 60°. The torque required to maintain the needle in this position will be:

    A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60^(@) . The torque needed to maintain the needle in this position will be