Question

Magnetic flux density and magnetic potential curl equation

Answer 1

Mass 5 velocity 100m/sec block upto 6cm

Answer 2

Firstly, how is the equation solved after taking the curl of A(r) here. How did they arrive at the final expression for B(r). Take the product rule for curl, but got two terms zero, as m doesn't depend on r, but couldn't get the expression given here by solving further.

A(r)=μ04πr3m×r

B(r)=∇×A=μ04πr3(3r(m⋅r)r2−m)

Secondly, how and why the vector potential described in the above link different from one of the "retarded potentials" shown here. They're both used to find B(r)

A(r,t)=μ04π∫J(r′,tr)|r−r′|d3r′

where tt=t−1c|r−r′|