Magnetic Field of Straight Wires
The magnitude of magnetic induction at mid point due to current arrangement as shown in Fig will be

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Answer: (a)
- AB and ED lie on the line through O, so they give zero field.
- BC and ET are semi-infinite wires starting at the foot of the perpendicular from O, each at distance : .
- Both point out of the page, so they add:
- So the answer is (a).