# Homework Help: Measuring the strength of the earths magnetic feild using the slope of a graph

1. May 24, 2007

### peyo

Hi, Kinda new here so here goes.

I have been asked to drawn a graph B(magnetic field) vs Tan theata and find its slope, ok no problem there. The next question has asked me to use the value of the slope to obtain the value of the strength of the earth's magnetic field in the region .

The context of the question is this:

There is a wire running north south along the earths magnetic field, 1cm above the wire is a needle that points to magnetic north when there is no current running along the wire. When current flows through the wire (northward) the needle deflects to the east, various different strength currents are passed through the wire and the angle of defection is recorded in a table along with the strength of the field in (microT), this table is then graphed and the slope obtained.

All that has been done, I've read the rulles and am not really looking for an answer more a method as I am drawing a blank. Any help would be greatly appreciated.

cheers

2. May 24, 2007

### Mentz114

Welcome to the forum. To do this problem you need to find a formula that relates the strength of a magnetic field to the deflection of a magnetic needle. You also need a formula to connect the current in a wire to the magnetic field strength around the wire. From your experiment, you can now work out how much current it takes to reverse the deflection caused by the earth's field, and hence the strength of that field.

3. May 25, 2007

### peyo

Yeap, thats great!! thankyou very much for the nudge:) somr times a good nights sleep and a friendly hint is what I need. I will be visiting here often.

cheers