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**we are given some component of a vector potential A**

[tex]

A = B\displaystyle\int^d_0 I(t')\,dt'

[/tex]

where d = t -z/c

and B = constant=1/2 mu0 (permeability constant) x c (speed of light)

[tex]

A = B\displaystyle\int^d_0 I(t')\,dt'

[/tex]

where d = t -z/c

and B = constant=1/2 mu0 (permeability constant) x c (speed of light)

the derivation then wants me to calculate the magnetic field from this vector potential which is

[tex]

\vec B = \nabla \times A = \frac{d\(A}{dz} \vec j

[/tex]

where d/dz is meant to be partial diff

the result that is arrived at is

[tex] \vec B = CI(t-(z/c))\vec j[/tex]

where

C= +/- 1/2 x(permeability constant)

the step eludes me. i was fine until this point. i tried hitting it with the chain rule, and i suspect that the solution involves this somehow.

p.s. i'm new to latex, so if you think some information is missing, or the equations are simply not showing, It'd be great if someone could tell me, cheers.

**1. Homework Statement**

**2. Homework Equations**

**3. The Attempt at a Solution**