1. The problem statement, all variables and given/known data A circular loop of radius R is on the xy plane and the center is at the origin, the current is flowing in a counter-clockwise manner. a) Let Q=(a,0,a) be a point such that a>>R. Find Br and Bθ at Q. b) Let Q=(ha,0,0) be a point on the x-axis such that h<1. Find the vector potential A at Q as a power series of h. 2. Relevant equations A(r) = k∫ (J(r') dτ') / |r-r'| = kI ∫ dr' / |r-r'| where k is μo/4π and I is the current 3. The attempt at a solution a) From azimuthal symmetry, we can restrict the situation to points r on the xz plane. dr'=(dx', dy', 0)=(-Rsinφ', Rcosφ', 0)dφ'. Since the only non vanishing component of A is Aφ Aφ(r) = kI ∫ (Rcosφ' dφ') / |r-r'| from 0 to 2π Bφ = 0 Br = - 1/r ∂/∂cosθ (Aφsinθ) Bθ = - 1/r ∂/∂r (rAφ) Is this correct? For part b) I don't know if it is a multipole expansion or somethin' else... Any help?