Fall 2018 Homework Assignments
For this homework, do not use any vector calculus theorems to simplify the algebra, complete
the differentiation and integration operations as instructed in the problems.
A tetrahedral volume V is defined by its 4 corners O, A, B and C with the x-y-z coordinates
O : 0, 0, 0
A : 1, 0, 0
B : 0, 2, 0
C : 0, 0, 3
The triangular surfaces S1, S2, S3 and S4 are defined by their corners
S1 : OAB
S2 : OAC
S3 : OBC
S4 : ABC
with their directions pointing outside V.
1) Find the unit vectors in the directions of S1, S2, S3 and S4.
2) Consider the function v(x,y,z) = xy2z3.
(a) Find its gradient E = ∇ v
(b) Find its laplacian ρ = ∇2 v
(c) Find the curl of E: C = ∇ x E
(d) Integrate ρ within the volume V: Q = ∫V ρ d3x
(e) Integrate E along the edge of surface S4: I = ∮ABCA E ⋅ dl
(f) Integrate E on the surfaces Si to find its flux through these surfaces: Φi = ∫Si E ⋅ dS
(g) What is the total flux Φ1 + Φ2 + Φ3 + Φ4 ?
3) Consider the vector field A = i xy2z3 + j xyz + k x2yz3
where i, j and k are the unit vectors in the x, y and z directions respectively.
(a) Find the curl of A : B = ∇ x A
(b) Find the curl of B : j = ∇ x B
(c) Find the flux of j through surface S4 : I4 = ∫S4 j ⋅ dS
(d) Integrate B along the edge of surface S4: i4 = ∮ABCA B ⋅ dl
We are interested in finding the potential within the part of space V given by
x>0, y>0 and all vales of z.
There is no charge in this region, but the potential at the boundaries is given by
On the surface at y=0: V = Vo for 0<x<a and 0<z<a
On all other parts of the boundary: V=0.
In other words, just a square area of dimensions a x a on the x-z plane is at
potential V = Vo and all other parts of the boundary are at zero potential.
Find the corresponding Green's function and write down an integral expression for the
potential at a general point inside V.

A grounded spherical shell of radius R is centered at the origin. A ring charge (with total charge Q) and radius r is centered on the z-axis a distance a from the origin. The plane of the ring is perpendicular to the z-axis. Find the potential on the z-axis for -R < z < R. Verify your solution for z = ±R.
Check the Stars system for your homework grade. In some cases, you may be able to re-submit your homework to the assistant with corrections and improve your grade.