- #1

Mysterious

- 5

- 0

## Homework Statement

A long, straight, copper wire has a circular cross section with radius R, resistivity p and permittivity ε. If the current through the wire at any time t is sin(ωt) amperes, find the magnitude of the magnetic field B at time t a distance r from the centre of the wire for r > R.

## Homework Equations

Ampere's Law:

μI = ∮

**B**•

**dl**

Possibly Law of Biot-Savart:

B = μ/4π * (I

**dl**x

**r**)/r^2

## The Attempt at a Solution

μI = ∮

**B**•

**dl**

μ(sin(ωt))=∮B*dl (Since they are parallel)

μ(sin(ωt))=B∮dl (Since B is constant radially around conductor)

This is where I reach a bottleneck. I don't know how to incorporate ε (since this is a magnetic field). I assume resistivity would be used in calculating the current I, but I don't know how that ties into the sinusoidal function.