Field at the centre of a hairpin: a semicircle joined to two long parallel straight wires

1. A.
   $\frac{\mu_{0}I}{4\pi r}(2 - \pi)$
2. B.
   $\frac{\mu_{0}I}{4\pi r}(2 + \pi)$
3. C.
   $\frac{\mu_{0}I}{2\pi r}(2 + \pi)$
4. D.
   $\frac{\mu_{0}I}{2\pi r}(2 - \pi)$

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1. A.
   $\frac{\mu_{0}i}{2r}\left( 1 + \frac{2}{\pi} \right)$
2. B.
   $\frac{\mu_{0}i}{2r}\left( \frac{1}{2} + \frac{1}{2\pi} \right)$
3. C.
   $\frac{\mu_{0}i}{2r}\left( 1 + \frac{1}{\pi} \right)$
4. D.
   $\frac{\mu_{0}i}{2r}\left( \frac{1}{2} + \frac{1}{\pi} \right)$

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