# Ampere's law problem help please

## Homework Statement

So a long straight wire lies on a horizontal table and carries a current of 1.2x10^-6A. In a vacuum, a proton moves parallel to the wire(opposite the current) with a constant speed of 2.3x10^4 m/s at a distance d above the wire. Determine the value of d. You may ignore the magnetic field due to the Earth.

## Homework Equations

ampere's law
F(magnetic field)=q(vxB)
Biot savart law?

## The Attempt at a Solution

So what I did is have the magnetic field formula for a wire, I then substitute this into the magnetic force equation. But now I don't really know where to go from there. Please help. Thanks very much.

Doc Al
Mentor
Hint: Since the proton moves with constant velocity, what must the net force be on it?

well net force should be zero but then would it mean F(magnetic)= mg or I am not sure what it would be equal to?

Doc Al
Mentor
well net force should be zero but then would it mean F(magnetic)= mg
You got it.

oh thanks very much