Show that the magnetic field at a point due to a magnetic dipole is perpendicular to the magnetic axis if the line joining the point with the centre of the dipole makes an angle of tan−1(√2) with the magnetic axis.
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Solution
Given:
θ=tan−1√2⇒tanθ=√2⇒2=tan2θ
⇒tanθ=2cotθ⇒tanθ2=cotθ
We know tanθ2=tanα
Comparing we get, tanα=cotθ
or, tanα−tan(90−θ) or
α=90−θ or
θ+α=90
Hence magnetic field due to the dipole is ⊥r to the magnetic axis.