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An infinite wire has a circular bend of radius a, and carrying a current I as shown in figure. The magnitude of magnetic field at the origin O of the arc is given by :

1. ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + π π μ 1 2 a I 4 0
2. ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + π π μ 1 2 3 a I 4 0
3. ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + π π μ 2 2 a I 2 0
4. ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + π π μ 2 2 3 a I 4 0

Correct answer: ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + π π μ 1 2 3 a I 4 0

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