Question

Why magnetic field lines appear straight in t spare center of circular loop?

Answer 1

The field lines around a current carrying wire are concentric circles. (To visualise better , look up the images for magnetic field lines aroung a straight wire and around a current carrying loop ) . At the center of the circle ,every field line is at an equal distance , thus they exert equal pressure on each other ,and bend each other into the same direction. While any other point inside the circle would be closer to one point as compared to another .