Homework Help: Direction of a current

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1. Aug 10, 2016

thaalescosta

• Thread moved from the technical forums, so no Homework Help Template is shown
This is the question:
At a certain location in the Philippines, Earth’s magnetic field of 39 µT is horizontal and directed due north. Suppose the net field is zero exactly 8.0 cm above a long, straight, horizontal wire that carries a constant current. What are the magnitude and direction of the current?

I had no problem finding the magnitude of the current, but I'm struggling with visualizing the direction of the current. I didn't really understand what "horizontal and directed due to north" meant.

Is anyone able to illustrate what is going on with the magnetic field and how the wire is affecting the field?

Thanks

2. Aug 10, 2016

composyte

Alright so your basic plan of attack is to use the right hand rule. If there is a magnetic field pointing north and there is a wire running perpendicular to it: in what direction must the current flow to have its magnetic field oppose the one already present? I hope this rephrasing helps you some.

3. Aug 10, 2016

thaalescosta

This is how I'm visualizing. The answer says the current flows from west to east, but I don't see how the magnetic field is being cancelled by the current.

4. Aug 10, 2016

Bystander

Map it by cm increments.

5. Aug 10, 2016

thaalescosta

what do you mean

6. Aug 10, 2016

Bystander

Eight cm, nine cm, ... seven cm.

7. Aug 10, 2016

thaalescosta

I know, but I don't see how that would help me with the visualization. I have it scaled on paper, but I still don't get why the direction of the current must go from west to east instead of the opposite

8. Aug 10, 2016

Bystander

Is the conductor above or below the zero-field height?

9. Aug 10, 2016

thaalescosta

The wire carrying the current is 8cm below the point where the net field is equal zero.

10. Aug 10, 2016

Bystander

Only at one point.