# Magnetic Field in an Infinitely Long Copper Rod

## Homework Statement

A long, solid, copper rod has a circular cross-section of diameter 10.0 cm. The rod has a current of 5.0 A, uniformly distributed across its cross-section. Calculate the magnetic field strength at:

a) the centre of the rod
b) 2.5 cm from the centre
c) 5.0 cm from the centre
d) 7.5 cm from the centre

## Homework Equations

This is supposed to be done somehow using B = μ/2∏ * I/r

I don't have any calculus knowledge.

## The Attempt at a Solution

I've tried many ways, but nothing has been consistent. I assume that I need to figure out the value of I at each different point of the copper rod, which I've tried doing through all this finicky work with area and all this stuff, but I truly don't understand what I'm doing.

Hey,
You stated that,
I don't have any calculus knowledge.
.
That's going to be very problematic, and a damper on your solving equations here;
You'll have to consider http://en.wikipedia.org/wiki/Ampere%27s_Law#Integral_form.
Also, remember that you're told that the current is distributed evenly across the cross section, or surface area, in other words, I' = (I/A)*A'(r), where A' is the local area, or, to be precise,
(I/R^2)*r^2, r<=R, where r is the distance from the center, and R=D/2;
So you ought to get, B*2*Pi*r=mu_0*(I/R^2)*r^2.
Master calculus, it's imperative,
Good luck,
Daniel