1.

The coercitivity of a small magnet where the ferromagnet gets demagnetized is `3 xx 10^(3) Am^(-1)`. The current required to be passed in a solenoid of length `10 cm` and number of turns `100`, so that the magnet gets demagnetized when inside the solenoid , is :A. ` 30 mA`B. ` 60 mA`C. `3 A`D. ` 6 A`

Answer» Correct Answer - C
Magnetic field in solenoid `B = mu_(0) n I `
rArr `(B)/( mu_(0)) = ni`
( where n = number of turns per unit length)
rArr `(B)/( mu_(0)) = (ni)/(L)`
rArr ` 3 xx 10^(3) = ( 100 i)/( 10 xx 10^(-2))`
` I = 3 A`


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