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# A straight wire of length $\ell$ carries a current $i$. The magnitude of magnetic field at the point $P$ is

$\begin {array} {1 1} (a)\;\large\frac{\sqrt 2 \mu_0i}{\pi l} & \quad (b)\;\large\frac{\sqrt 2 \mu_0i}{2\pi l} \\ (c)\;\large\frac{\sqrt 2 \mu_0i}{4\pi l} & \quad (d)\;\large\frac{\sqrt 2 \mu_0i}{8\pi l} \end {array}$

$\overrightarrow B = \large\frac{\mu_0i}{4 \pi l}$ $( \sin \alpha + \sin \beta)$
Here $\alpha = 0^{\circ} \: and \: \beta = 45^{\circ}$
Ans : (d)