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The mass of a magnetic needle is 7.5 g a...

The mass of a magnetic needle is 7.5 g and its magnetic moment is 98 units . To keep the magnetic needle horizontal in the northern hemisphere , what should be the position of its fulcrum with respect to its Centre of gravity ? Vertical component of earth's magnetic field = 0.25 Oe .

Text Solution

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Let the fulcrum be kept at a distance x (towards the north pole ) from the centre of gravity to keep the magnetic needle horizontal [ Fig]
If the length of the magnetic needle = 2 l and the strength of each pole = m , magnetic moment , `p_(m)=m. 2l.`
`therefore` In equilibrium,
`mV.2l=W.x`
`"or , "V.p_(m)=W.x`
`"or, "x=(V.p_(m))/(W)=(0.25xx98)/(75.980)=0.0033 "cm"`
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