Unsure About the Right Hand Rule? Get Help Here!

[minimario]

Homework Statement

Homework Equations

Right Hand Rule

The Attempt at a Solution

I can get the magnitude, but cannot get the directions from the RHR. Can somebody make video/explain?

Thanks!

 

[berkeman]

Homework Statement

Homework Equations

Right Hand Rule

The Attempt at a Solution

I can get the magnitude, but cannot get the directions from the RHR. Can somebody make video/explain?

Thanks!

Can you post a sketch and your work please? That will help us help you figure this out. Thanks.

 

[minimario]

It is just the right hand rule...what "sketch" is there?

 

[berkeman]

It is just the right hand rule...what "sketch" is there?

The problem statement involves a 3-dimensional problem. The solution involves a sketch with 3-d coordinates and calculations. Are you asking us to reproduce all of your work in order to help you? Please post your detailed sketch and calculations so that we can help you.

 

[minimario]

I don't need the magnitude part. I need the direction part... and 3d coordinates are not needed, the right hand rule is.

 

[berkeman]

I don't need the magnitude part. I need the direction part... and 3d coordinates are not needed, the right hand rule is.

You are not helping. I'm out. Hopefully somebody else can help you.

 

[minimario]

?? What do you mean?

 

[haruspex]

Quote the right hand rule, as it applies to a moving charge in a magnetic field.
Alternatively, quote the equation as a cross product and quote the rule as it relates to cross products.

 

[uselesslemma]

I don't need the magnitude part. I need the direction part... and 3d coordinates are not needed, the right hand rule is.

I think you need a refresher on the right hand rule. You may find the first sentence useful.

http://en.wikipedia.org/wiki/Right-hand_rule

The right-hand rule is defined for use in 3D coordinates. Furthermore, you should generally begin any physics problem by defining a convenient set of coordinates.

 

[minimario]

Right hand rule: point thumb in direction of v, fingers in direction of B, then F is direction of palm.

 

[uselesslemma]

Then what is your question?

 

[minimario]

I cannot get the direction.. do you have a picture of your right hand?

 

[uselesslemma]

 

[minimario]

I meant, in the position of this problem, with thumb, fingers oriented in position

 

[haruspex]

point thumb in direction of v, fingers in direction of B, then F is direction of palm.

So point your right thumb in the direction of the current (which way is that?) and your fingers in the direction of the field (which way is that?)

 

[minimario]

I cannot bend my hand so far...

 

[haruspex]

I cannot bend my hand so far...

At least answer my questions about directions, or I too will quit the thread. You are not trying very hard to help others help you.

 

[minimario]

Oh, I already know those ones, it's trivial. Current goes toward east, magnetic field is 75 degrees below horizontal...

 

[haruspex]

Oh, I already know those ones, it's trivial. Current goes toward east, magnetic field is 75 degrees below horizontal...

... but what direction is the magnetic field geographically?

 

[minimario]

Would be 75 degrees downward

 

[haruspex]

Would be 75 degrees downward

That's not a geographical direction. N, S, E, W...?

 

[minimario]

South

 

[haruspex]

South

So point your thumb E, your fingers S and 75 degrees down, with your hand flat. Which way is your palm facing?

 

[minimario]

Toward the north and down?

 

[haruspex]

Toward the north and down?

Yes. Down at what angle?

 

[minimario]

15 degrees below the vertical?

 

[haruspex]

15 degrees below the vertical?

Right.

 

[minimario]

No, it's not right, according to the answer key: answer says 15 degrees above horizontal in the north south plane

 

[haruspex]

No, it's not right, according to the answer key: answer says 15 degrees above horizontal in the north south plane

Ah yes, I slipped up.
The direction of Earth's magnetic field is towards the North. That's the way the North pole of a magnetic compass points. This means that considering the Earth as a magnet, its North pole is in the geographic South. Confusing isn't it?

 

[minimario]

It's 75 degrees below horizontal, so why is it north instead of south?

 

[haruspex]

It's 75 degrees below horizontal, so why is it north instead of south?

It doesn't depend on the dip angle.
The direction of the magnetic field of a dipole is defined, by convention, to be out of its North pole into its South pole.
The North pole of a magnet is defined to be the end which is attracted to somewhere near Earth's geographic North.
But the North pole of one magnet is attracted to the South pole of another. It follows that regarding Earth as a magnet, its North pole is at its geographic South pole, and vice versa.
To put it another way, the North pole of a compass needle points in the local direction of the Earth's magnetic field, i.e., approximately geographic North.
(In the context of the question, the 75 degree dip means we're at a high northern latitude.)