# Calculating the direction of Earth's magnetic field

1. Mar 17, 2013

### SnapDragon

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

Calculate the direction of Earth's magnetic field.

2. Relevant equations

3. The attempt at a solution

3 components of the magnetic field:

Geographic South to North: 0.01670 mT
Geographic West to East: 0.002147 mT
Up to down (up is the sky, down is the ground): 0.03722 mT

Calculating angle East of North:

tanθ=0.002147/0.01670
θ=7.33° East of North

Angle below horizontal:

tanθ=0.03722/√(0.016702+0.0021472)
θ=65.66° below horizontal

Is my attempt correct?

Last edited: Mar 17, 2013
2. Mar 17, 2013

### SnapDragon

If I did the first question correctly, I need help with this question:

Compare the direction of the projection of this magnetic field vector on the horizontal
plane (the angle to the east (or west) of geographic north) with the direction of the
compass.

I honestly don't understand what they're asking here. Are they saying to compare 7.33° with the direction of the compass? How do I find the direction of the compass?

3. Mar 17, 2013

### SnapDragon

Also, one last question:

The magnetic field in anywhere between two helmholtz coils is uniform, right?

4. Mar 17, 2013

### SnapDragon

Anybody? This is due tomorrow. :|

5. Mar 17, 2013

### haruspex

Your answer looks fine. I am similarly bemused by the second question. Since it says "the compass", I would expect it to be in the context of some actual compass described or supplied elsewhere.

6. Mar 17, 2013

### SnapDragon

Maybe they're asking to check the percent error compared to the real value?

7. Mar 17, 2013

### haruspex

It's not a percent error.
By 'real' value, do you mean true north, or the known declination for where you are?

8. Mar 17, 2013

### SnapDragon

9. Mar 17, 2013

### SnapDragon

I have no idea.

Don't worry about it. I'm just going to hand in what I have. No point stressing over it since no other students seem to know the answers either.

10. Mar 17, 2013

### haruspex

When you fill in the data table for e.g. the NS field, how are you determining that it's NS? Do you use the compass for that? If so, are you taking it from the magnetic N according to the compass, or are you correcting for declination?

11. Mar 17, 2013

### SnapDragon

Yes.

I am taking it from the magnetic N according to the compass.