The coercivity of a certain permanent magnet is `4.0xx10^(4)Am^(-1)`. The magnet is placed insider a solenoid 20cm long having 700 turns and a current is passed in the solenoid to demagnetise it completely. Find the current
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The corecivity of `4xx0^(4)Am^(-1)` of the permanent magnet implies that a magnetic intensity `H=4xx10^(4)Am^(-1)` is required to be applied in opposite direction to demagnetise the magnet Here `n(700)/(20cm)=(700)/((20xx10^(-2)m))=3500 "turns/m"` `As " " H=nI` `therefore Current,I=(H)/(n)=(4xx10^(4))/(3500)=11.5A`
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