1.

The coercivity of a small magnet where the ferromagnet gets demagnetised is 3 xx 10^(3) A//m. The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetised when placed inside the solenoid is

Answer»

30 mA
60 mA
`3 A`
`6 A`

Solution :The value of the reverse magnetising field required to make the residual magnetism of a sample equal to zero is called coercivity.
The coercivity of `3 xx 10^(3) A//m` of the MAGNET implies that a magnetic field of intensity `H = 3 xx 10^(3) A//m` should be APPLIED in opposite direction to demagnetise the magnet.
For a solenoid, `B = mu_(0)H` but `B = mu_(0)H`
`therefore H = ni`
In this case , `N = (1000)/(10cm)= (100)/(10xx10^(-2)m) = 1000 "turns"//m`
`:. i = H/n = (3 xx10^(3))/(1000) = 3A`


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