6.8 Curl operator in general coordinates (ψ,πœƒ,ΞΆ)

To take the curl of a vector, it should be in the covariant representation since we can make use of the fact that βˆ‡Γ—βˆ‡Ξ± = 0. Thus the curl of A is written as

βˆ‡ Γ— A = βˆ‡ Γ— (A1βˆ‡Οˆ + A2βˆ‡ πœƒ+ A3βˆ‡ ΞΆ)
      = βˆ‡(A1 Γ— βˆ‡ ψ+ βˆ‡A2  Γ—) βˆ‡πœƒ+ βˆ‡A3( Γ— βˆ‡ΞΆ           )        (                )
          βˆ‚A1-    βˆ‚A1-             βˆ‚A2-     βˆ‚A2-             βˆ‚A3-     βˆ‚A3-
      =   βˆ‚πœƒ βˆ‡ πœƒ+  βˆ‚ΞΆ βˆ‡ΞΆ  Γ— βˆ‡ ψ+    βˆ‚Οˆ βˆ‡Οˆ +  βˆ‚ΞΆ βˆ‡ΞΆ  Γ— βˆ‡ πœƒ+   βˆ‚Οˆ βˆ‡ ψ+  βˆ‚πœƒ βˆ‡ πœƒ  Γ—βˆ‡ ΞΆ
        1 ( βˆ‚A2   βˆ‚A1 )             1 (βˆ‚A1   βˆ‚A3 )             1 ( βˆ‚A3   βˆ‚A2)
      = π’₯-  βˆ‚-ψ-βˆ’ -βˆ‚πœƒ- π’₯ βˆ‡ ΟˆΓ— βˆ‡ πœƒ+ π’₯-  -βˆ‚ΞΆ-βˆ’ -βˆ‚Οˆ-  π’₯βˆ‡ ΞΆ Γ— βˆ‡ ψ + π’₯  βˆ‚πœƒ--βˆ’ βˆ‚-ΞΆ- π’₯ βˆ‡πœƒ Γ—(1βˆ‡1ΞΆ6.)
Note that taking the curl of a vector in the covariant form leaves the vector in the contravariant form.