Length of the vector (electrostatic cylinder)

by Blastrix91
Tags: cylinder, electrostatic, length, vector
Blastrix91 is offline
Nov19-12, 10:04 AM
P: 25

My problem is that I'm confused about a hint I was given in this problem. I usually use the law of cosine to find the length of [itex]\vec{r}-\vec{r'}[/itex]. But the hint here says that I should make it [itex][r^2 + (z - z_0)^2]^{1/2}[/itex]

Where does this come from? I can't quite get my head around the geometrical idea of this hint. Can't the law of cosine be used here?
Phys.Org News Partner Physics news on Phys.org
Better thermal-imaging lens from waste sulfur
Scientists observe quantum superconductor-metal transition and superconducting glass
New technique detects microscopic diabetes-related eye damage
mikeph is online now
Nov19-12, 10:16 AM
P: 1,199
It's really hard to answer these questions when you don't specify what any of the terms mean, so I can only guess at what r-r' even is. It looks like a Pythagoras approach to give you the hypotenuse of the triangle with sides r and z-z0.

How would you use the law of cosine, and what problem would using it solve?
nasu is offline
Nov19-12, 01:26 PM
P: 1,903
I don't know how the hint is specifically formulated but I think the best way here is to use cylindrical coordinates.
It may be that r' is the cylindrical radius of the charge element.
The point P has r=0 and z=zo.

Register to reply

Related Discussions
Moment of inertia of hollow cylinder, axis orthogonal to length Classical Physics 4
Gauss's law, cylinder of length L Introductory Physics Homework 6
Casimir effect and a finite length Tipler cylinder? General Physics 0
Solve for the length of a cylinder Introductory Physics Homework 2