# Homework Help: Magnetic Fields

1. Oct 3, 2011

### jsmith613

1. The problem statement, all variables and given/known data

At a certain point on the Earth's Surface the horizontal component of the earths magnetic field is 1.8 * 10^-5 T. A straight piece of wire 2m long and 1.5g lies on a horizontal wooden bench in an east-west direction. When a very large current flows momenterily in the wire it is JUST enough to cause the wire to lift off the bench surface.
State the direction of the current in the wire.

2. Relevant equations
NONE
Use left-hand rule
3. The attempt at a solution
What I don't understand is how we can use the left hand rule given the information. We don't know the direction of the magentic field (we were only given the horizontal componenet - i.e there is a vertical component too)

How is this done
(if it helps the answer is east)

2. Oct 3, 2011

### jsmith613

does it have anything to do with the fact that the only magnetic field is horiztonal because the only force is up

3. Oct 3, 2011

### SammyS

Staff Emeritus
What do you know about the direction of Earth's magnetic field ?