Need help with this simple question!

[Linkage1992]

http://i54.tinypic.com/2wrn1i8.jpg

So the answers west, but i cannot for the life of me get that answer. Every time I picture the earth, the magnetic field is going upwards and the current would be heading into the centre of the earth, and when I apply the right hand slap rule I always get my palm pointing in the easterly direction. What am I doing?? 

[m@tty]

You need to know that geographical north is magnetic south and because electrons are flowing DOWN, the current is effectively up.

So now use the right hand slap rule: fingers north and thumb up - you get a slap to the left. Now remembering that forward was north, you can deduce that left is west.

[Linkage1992]

Ah, of course! the current is up *facepalm*

thanks! hopefully i don't do this stupid shit in the actual exam.

edit: and the stupid answers were misleading. they said the current was going down the rod in their 'reasoning', so that added to my confusion a bit.

[3Xamz]

But how do we know that when they say "horizontal" its left to right? Couldn't it equally be right to left?

EDIT: Nvm, I got it.

[qshyrn]

But how do we know that when they say "horizontal" its left to right? Couldn't it equally be right to left?

EDIT: Nvm, I got it.

can someone explain this further? i havent got it yet    how do u know the magnetic field is going into the page.?

[3Xamz]

Nah they say its going horizontal right?
So let's assume the geographical north pole is at the left side of the page and the geographical south pole is one the right.

That means the magnetic north pole is on the right, and the magnetic south pole is on the left. (Since they are reversed, geographical poles and magnetic poles.)

This means the field lines are going from RIGHT to LEFT.

Current is going UP the pole.

Point your fingers from right to left, thumb should be straight up.
This would give a force OUT the page.

Now we predefined the geographical north pole is on the left and geographical south pole to be on the right. So, if we have a force direction OUT OF page, it must be West.

[qshyrn]

Nah they say its going horizontal right?
So let's assume the geographical north pole is at the left side of the page and the geographical south pole is one the right.

That means the magnetic north pole is on the right, and the magnetic south pole is on the left. (Since they are reversed, geographical poles and magnetic poles.)

This means the field lines are going from RIGHT to LEFT.

Current is going UP the pole.

Point your fingers from right to left, thumb should be straight up.
This would give a force OUT the page.

Now we predefined the geographical north pole is on the left and geographical south pole to be on the right. So, if we have a force direction OUT OF page, it must be West.

oh ok i get it know.. it didnt matter which way we defined North.

[3Xamz]

Yeah, depending on which way you defined north/south you'd either get a force into/out of the page.

Both in relation to your predefined poles would point to west.

[TyErd]

really good explanation qshyrn. I always mucked up these type of questions, now i wont thanks!