1.

Let `r` be the distance of a point on the axis of a magnetic dipole from its centre. The magnetic field at such a point is proportional toA. 16AB. 8AC. 4AD. 2A

Answer» Correct Answer - B
The coercivity of bar magnet `4xx10^(3)A-m^(-1)` Length of solenoid=12cm, Number of turns=60
The coercivity of 12cm length of solenoid
`" " 4xx10^(3)xx12xx10^(-2)=480`
Now, current through each turn to demagnetise =`(480)/(60)=8A`


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