2. The current distribution of an infinite, wire can be described in cylindrical coordinates by J = J(p) 2. longitudinally-uniform, and axially-symmetric (a) Show that · J = 0. (b) Considerations of longitudinal and axial symmetry require that the mag- netic field can only depend upon p, i.e. that B(p) = B₂(p)ô + Bø(p)ô + B₂(p)2. Use Ampère's Law to determine B6 (p) in terms of I (p) = 2π J(p') p'dp'. (c) Use the Biot and Savart Law to show that Bp(p) = B₂ (p) = 0. Side note: it is pretty easy to show that B,(p) must be zero using Gauss's Law for B with a cylindrical volume. I am not aware of an "easy" way to see B₂ (p) = 0 - not that it is very difficult using the Biot and Savart Law... (d) Use the integral form for the vector potential [Jackson, Eq. (5.32)] to determine A for this current distribution. Hint: in order to deal with divergent integrals, you may want to limit the current distribution to -L ≤ z ≤ L, determine A, adjust A by a constant (as one is allowed to do), and then take L→ ∞. (e) Verify that the A in part (d) reproduces the B found in parts (b) and (c) when the curl is taken.

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longitudinally-uniform, and axially-symmetric
2. The current distribution of an infinite,
wire can be described in cylindrical coordinates by
J = J(p)ź.
(a) Show that · ƒ = 0.
(b) Considerations of longitudinal and axial symmetry require that the mag-
netic field can only depend upon p, i.e. that
=
Ẻ(p) = B₂(p)ô+ Bø(p)❖ + B₂(p)ź.
Use Ampère's Law to determine Bo(p) in terms of I(p) = 2π ff J(p') p'dp'.
(c) Use the Biot and Savart Law to show that Bp(p) = B₂ (p) = 0. Side note:
it is pretty easy to show that Bp(p) must be zero using Gauss's Law for
B with a cylindrical volume. I am not aware of an "easy" way to see
B(p) 0 not that it is very difficult using the Biot and Savart Law...
(d) Use the integral form for the vector potential [Jackson, Eq. (5.32)] to
determine A for this current distribution. Hint: in order to deal with
divergent integrals, you may want to limit the current distribution to
-L≤ z <L, determine Ã, adjust à by a constant (as one is allowed to
do), and then take L→ ∞.
(e) Verify that the à in part (d) reproduces the B found in parts (b) and (c)
when the curl is taken.
Transcribed Image Text:longitudinally-uniform, and axially-symmetric 2. The current distribution of an infinite, wire can be described in cylindrical coordinates by J = J(p)ź. (a) Show that · ƒ = 0. (b) Considerations of longitudinal and axial symmetry require that the mag- netic field can only depend upon p, i.e. that = Ẻ(p) = B₂(p)ô+ Bø(p)❖ + B₂(p)ź. Use Ampère's Law to determine Bo(p) in terms of I(p) = 2π ff J(p') p'dp'. (c) Use the Biot and Savart Law to show that Bp(p) = B₂ (p) = 0. Side note: it is pretty easy to show that Bp(p) must be zero using Gauss's Law for B with a cylindrical volume. I am not aware of an "easy" way to see B(p) 0 not that it is very difficult using the Biot and Savart Law... (d) Use the integral form for the vector potential [Jackson, Eq. (5.32)] to determine A for this current distribution. Hint: in order to deal with divergent integrals, you may want to limit the current distribution to -L≤ z <L, determine Ã, adjust à by a constant (as one is allowed to do), and then take L→ ∞. (e) Verify that the à in part (d) reproduces the B found in parts (b) and (c) when the curl is taken.
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