2.35 Show that if F is a conservative field, then ∇2 F ¼ ∇(∇F). Use cylindrical coordinates.
2.36 Given the scalar field f (x,y,z) ¼ 2x2 + y and the vector field R ¼ ^x x þ ^y y þ ^z z, find:
(a) The gradient of f.
(b) The divergence of f R.
(c) The Laplacian of f.
(d) The vector Laplacian of R.
(e) The curl of fR.
2.37 A vector field A ¼ ^x 5x þ ^y 2y þ ^z 1. What type of field is this according to the Helmholtz theorem?
2.38 A vector field A ¼ ^R ϕR2 þ ^θ Rsinθ is given in spherical coordinates. What type of field is this according to the
Helmholtz theorem?
2.39 The following vector fields are given:
(1) A ¼ ^x x þ ^y y:
(2) B ¼ ^ϕ cosϕ þ ^r cosϕ:
(3) C ¼ ^x y þ ^z y:
(4) D ¼ ^R sinθ þ ^θ 5R þ ^ϕ Rsinθ:
(5) E ¼ ^R k:
Problems 93
(a) Which of the fields are solenoidal?
(b) Which of the fields are irrotational?
(c) Classify these fields according to the Helmholtz theorem.
2.40 Show by direct derivation of the products that the following holds:
∇ ð∇ AÞ ¼ ∇ ∇A ð Þ∇2A: