# Can someone explain the Earth's magnetic field to me?

1. Oct 21, 2009

### Suy

I don't really understand how the Earth's Magnet work. For example, when the question say the electron is moving horizontally to the east. And then i asked someone, they said the horizontal actually is the vertical. And why does the magnetic field go from south to north, isn't north to south? is the earth magnetic field line straight?
How would you compare if the lightning strike a beam of electron at the equator or at the pole??
How would you apply the hand rule to determine the direction of electron traveling horizontally?
If someone could explain the concept to me. Btw, i have a test tomorrow, if anyone can explain this to me today.
thank you very much.

2. Oct 21, 2009

### trini

think of the earth as a bundle of charge. because the earth spins from west to east, if you were to look at the earth from top at the north pole, the earth's rotation, and thus the charges the earth is made up of, would be anti clockwise. flemming's right hand grip rule does the rest.

3. Oct 21, 2009

### Suy

Can you explain it a little more? And answer some of my question.
actually, the main thing is that i don't know how to use the hand rule to apply on a circular magnetic field...
ty!

4. Oct 21, 2009

### trini

think of just the equator, think of the circle it describes as being a circuit loop. current is flowing around the loop anticlockwise, so by Flemming's RHGR, the net magnetic field is always pointing up towards the north pole inside the loop.

just remember for the circular loop, you apply the grip rule at the tangent at that point, i think thats what you were asking

5. Oct 22, 2009

### Suy

Yes, that's make sense to me now. So the direction of magnetic field is downward.
But how do you use hand rule to determine to deflected direction?
Like ,if the electron is traveling horizontally from west to east at the equator, what is the direction of deflected force?
I used the left hand for electron, the thumb point east , the finger point downward, the palm is pointing out of the page(pointing toward me).
but the answer in my text book is downward toward Earth's surface. I don't know why..

6. Oct 22, 2009

### Suy

7. Oct 22, 2009

### espen180

You have to use your right hand or the Right Hand Rule won't work...

8. Oct 23, 2009

### Suy

ok, but even i used the right hand rule, i still got the same result...

9. Oct 23, 2009

### espen180

The direction of the field is north. The direction of the particle (negatively charged) is east.

$$\vec{v}\times\vec{B}$$ is downward.

The magnetic force on the particl is $$q\vec{v}\times\vec{B}$$. $$q$$ is negative, so the force points up, away from the earth.