Sol. At an arbitrary point on line AB any small element of current of conductor ACB induces a magnetic field perpendicular to the plane of the drawing (see question 1). The element of conductor ADB symmetrical to it induces the same field, but directed oppositely. For this reason the field from any two elements arranged symmetrically will be zero. Hence, the field at the arbitrary point on AB induced by the entire conductor is zero, since the straight sections of the conductor also do not induce a field on AB.