What Are the Correct Directions for the Forces in These Diagrams?

[shimizua]

Homework Statement

Decide from the following list of possibilities what is the appropriate direction of the force on the wire for each of the diagrams 1 through 4:


A: up; B: down; C: left; D: right; E: into the page; F: out of the page; G: None of these; H: No force


Input the answers for diagrams 1-4 as they are posed - no spaces, no commas. For example if the force on diagram 3 is into the page and there is no force on any of the other wires then input 'HHEH'.
1.
http://capa-new.colorado.edu/teacher/capalibrary/Graphics/Gtype61/prob20v8.gif
2.
http://capa-new.colorado.edu/teacher/capalibrary/Graphics/Gtype61/prob20v1.gif
3.
http://capa-new.colorado.edu/teacher/capalibrary/Graphics/Gtype61/prob20v3.gif
4.
http://capa-new.colorado.edu/teacher/capalibrary/Graphics/Gtype61/prob20v6.gif

Homework Equations

well i used the right hand rule and came up with BAEG but don't know what i did wrong. Not too good with the right hand rule

The Attempt at a Solution

 

[eliasbagley]

This is the way I learned it: F = IlxB , where I is the current, l is the length (direction too, since it is a vector quantity), and B is the magnetic field, with the cross product operation.

So for figure 1: point the fingers of your right hand in the direction of I, and point your palm in the direction of B. The direction of your thumb will be the direction of the force. So the force will be UP.

Figure 2: fingers in the direction of I, palm in the direction of B, so the force is OUT.

Figure 3: fingers in the direction of I, palm in the direction of B, force points in the direction of the thumb: the force is DOWN.

Figure 4: fingers of the right hand in the direction of I, palm in the direction of B, thumb points in the direction of the force: so the force is IN.

Alternatively, you can think of it as the direction a screw would advance if you put the tails of the two vectors together, and screwed I in the direction of B through the smaller angle.

Hope this helps.

 

[shimizua]

hey thanks that was right. i really hate right hand rule stuff

 

[eliasbagley]

It's really simple stuff. Just point your fingers and palm in the right direction, and you've got the direction of the force. It all comes from the formula with the cross product.

And always remember to use your right hand, or you'll have the force in the wrong direction. It is the right hand rule, after all.