# Homework Help: Force between two long parallel conductors

1. Apr 16, 2010

### logearav

1. The problem statement, all variables and given/known data

revered members,
in the attachment given by me, B1 acts perpendicular to the plane of paper and inwards and B2 acts perpendicular to the plane of paper and outwards.
1)my assumption is due to magnetic lorentz force they are acting perpendicular . but why B1 acts inwards and B2 acts outwards.
2) also, it has been mentioned by fleming's left hand rule, F acts towards left, that is F due to current carrying conductor AB and by the same rule F acts towards right, that is F due to current carrying conductor CD.
according to fleming's left hand rule thumb will represent the direction of force, forefinger represents direction of magnetic field and middle finger represent the direction of current. but when i point my forefinger in the direction of current on AB my thumb points towards the left of AB. then how force due to AB point towards the right of AB. but it works fine when i do the same thing to the conductor CD when i point the forefinger in the direction of current.
my physics sir told that it is due to newton's third law AB's force points towards CD and CD's force points towards AB. but how fleming's left hand rule applied here. please help
2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### IMG.jpg
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2. Apr 16, 2010

### collinsmark

Hello logearav,

You can use the right hand rule for this. Put your right hand thumb in the direction of the current, and your fingers curl around in the direction of the field. http://www.websmileys.com/sm/fingers/fing04.gif

A couple things to note on the figure. B1 is shown "attached" to the CD wire (I2), but keep in mind that B1 is caused by the AB wire (I1). similarly, B2 is caused by I2, even though the vector is attached to I1 wire in the figure.
http://www.websmileys.com/sm/fingers/fing10.gif

I don't think you're using the left hand rule properly. Point your index finger in the direction of the field, not the current. You middle finger points in the direction of the current. http://www.websmileys.com/sm/fingers/fing32.gif

Last edited: Apr 16, 2010
3. Apr 18, 2010

### logearav

thanks a lot sir. excellent explanation.