Question

Help with a physics question I'm confused on :
6 m section of wire carries current of 5.2 A from east to west in earth's magnetic field of 1 × 10^-5 T . Which direction does the magnetic force act on wire?

Answer 1

Haha, I see you. I need to read the question, yet.

Answer 2

So, can you think of a relevant equation?

Answer 3

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html#c1

Answer 4

Oh! Do you know about the right hand rule for the cross product?

Answer 5

I've done a preview of it in class but we're supposed to start next week, it's just that I'm getting a little ahead because I think this might be a tougher topic so I want a few more days with it

Answer 6

Okay, sounds like a good idea.
Do you know about the cross product for vectors, yet?

Answer 7

That hyperphysics.phy-astr.gsu.edu site is good for finding many equations, by the way. :)

Answer 8

The key to understanding the direction is the cross product.

Did you learn about angular momentum? The angular momentum is perpendicular to both the radius and tangential velocity. You can find it by using the cross product,
\(\vec L=\vec r\times m\vec v\)
And this means you can use the "right hand rule" to find the direction of the angular momentum vector.

Torque is the same way, \(\vec \tau=\vec r\times\vec F\)

The force on a moving charge in a magnetic field...
And similarly the force on a current in a magnetic field...
Can be given by the cross-product, too.
So, just like angular momentum, and like torque, you can find the direction of the electromagnetic force. But the electromagnetic force direction makes more sense because you notice the force actually pushing that way.

So, do you know the right hand rule for the cross product?

Answer 9

Ooohhhh it's cool. Because it's easy! You have a right hand, correct? I hope so. It makes it easier.

Answer 10

haha yes

Answer 11

It might also help to have a diagram of your vectors, so I'll provide one now:

So, point your fingers straight out.

Now, position your hand so that your stretched out fingers are pointing in the direction of the first vector in the cross product.

Curl your fingers (not all the way), keeping your palm still.

For this next part, you might have to turn your wrist.
Now rotate your hand so that your curled fingers point in the direction of the second vector in the cross product.

Stick out your thumb. That is the direction of the cross product vector!

Our first vector is the current.
Our second vector is the magnetic field.
Our cross product is force and its direction is then....

Answer 12

The cross product will always be orthogonal (orthogonal is like perpendicular, but you don't need an intersection for things to be orthogonal) to the two vectors that were cross multiplied.

Answer 13

I think it should be up. I have to go! Good luck! That link shows the right hand rule in use. You can also research the right hand rule.

Answer 14

Hi! How's it going?

Answer 15

pretty good :) I have one other question I found intriguing and it has to do with a drawing :

Answer 16

Okay! This time we look at a different aspect of electromagnetic force.
Before, the moving charge felt a force because of an external magnetic field.
Now we look at something we didn't consider before.

Flowing charges actually create a magnetic field, and the current's magnetic field interacts with the compass.
Does that make sense, to start with?

Answer 17

yes :)

Answer 18

Okay! So now we need to learn what the direction of the magnetic field due to the current would be.

Right hand rule! This one is not really the right hand rule so much, though. I don't know why it works. BUT! You can point your right thumb in the direction of current. And then you can curl your fingers, and that's the direction the the magnetic field sort of spins around the wire.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecur.html#c1

Answer 19

Now, the direction of the field is like an arrow. It points in a direction. It starts from one end and goes to the other. For the magnetic direction, we say it starts at north and ends at south!

Answer 20

Let me know if you need clarification on anything.

Answer 21

This is like on a magnet. The north side emits them - it's where the magnetic field "lines" start. Think of the lines as sort of a way to imagine the direction of magnetic field vectors. Like, in the problem, there was a magnetic field vector directly south. At any point in our 3D world, there is a vector that says which way the magnetic field points.

The south side is where the magnetic field lines end.