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A ring of mass 'm' and radius 'r' carry...

A ring of mass 'm' and radius 'r' carrying current `i_(0)` is lying in the X-Y plane with centre at origin. A uniform magnetic field of strength `B=B_(0) (2hat(i)-3hatj+5hatk)T` is applied in the region. If the ring rotates about the axis .initial magnetic energy stored in the ring will be. (In joules)

A

`-pi^(2)i_(0)B_(0)`

B

`-5pir^(2)i_(0)B_(0)`

C

`-3pir^(2)i_(0)B_(0)`

D

`-2pir^(2)i_(0)B_(0)`

Text Solution

Verified by Experts

The correct Answer is:
B
`vec(M)=pir^(2)i_(0)hat(k)`
`vec(B)=B_(0)(2hat(i)-3hat(j)+5hat(k))`
`U=-vec(M).vec(B)`
`U=-5pi^(2)i_(0)B_(0)`
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