A current $i$ is flowing in a straight conductor of length $L.$ The magnetic induction at a point on its axis at a distance $\frac {L}{4}$ from its centre will be
A$\frac{{4{\mu _0}i}}{{\sqrt 5 \pi L}}$
B$\frac{{{\mu _0}i}}{{2\pi L}}$
C$\frac{{{\mu _0}i}}{{\sqrt 2 L}}$
D$Zero$
JEE MAIN 2013, Medium
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A$\frac{{4{\mu _0}i}}{{\sqrt 5 \pi L}}$
a $B=\frac{\mu_{0} i}{4 \pi R}\left(\sin \theta_{1}+\sin \theta_{2}\right)$
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