In the picture below, the two wires carry current i1 and i2, respectively, with positive current to the right. The charge q is positive and has velocity v to the right.

Question

anonymous · Answer

If i2 = 0 and i1 is greater than zero, then the magnetic field near charge q points out of the page. 
 If i2 = 0 and i1 is greater than zero, then the force on q points into the page. 
 If v = 0, then the force on q is zero. 
 If i1 = i2, then the wires are attracted to each other. 
 If i2 = - i1 then the force on q equals zero. 
 If i2 = 0 and i1 is greater than zero, then the force on q is north. 
 If i1 is greater than i2, then the force on q is north.

anonymous · Answer

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anonymous · Answer

Please Help! I have tried so many times!

anonymous · Answer

It would be false right? it would go into the page?

aum · Answer

Correct.  First choice is false.

anonymous · Answer

The second is false as well?

aum · Answer

Force will be in the direction of V cross B.

anonymous · Answer

The third and fourth ones are true im pretty sure as well

aum · Answer

I think so.

anonymous · Answer

do you know the last three by chance?

aum · Answer

f i2 = - i1 then the force on q equals zero. 
The magnetic field at q will be equal and opposite and will cancel each other out (assuming the charge is right at the center between the two wires).  Then the forces will cancel out.

aum · Answer

If i2 = 0 and i1 is greater than zero, then the force on q is north. 
Force will be in the direction of V cross B.

aum · Answer

You can use the fact that force on the charge will be in the direction of V cross B to figure out answers to the last two questions.

First use the right hand rule to figure out the direction of B at the location of charge q.  Then use right hand rule again to figure out the direction of V cross B.

anonymous · Answer

I am still confused

aum · Answer

If i2 = 0 and i1 is greater than zero, then the force on q is north.

What is the direction of the magnetic field due to i1 ?
Use the right hand rule.  Thumb of the right hand in the direction of the current and the curling of the fingers will be the direction of the magnetic field.  So at charge q, the direction of the magnetic field is into the page.
The direction of the force on the charge will be in the direction of V X B.  Apply right hand rule again with the fingers of the right hand curling in the direction from V to B.  Start out with fingers of the right hand pointing in the direction of V, which is to the right of the page.  Now curl the fingers towards B (B goes into the page).  The thumb will be pointing up or in the North direction.  

So this answer choice is True.

Use the same logic for the last part.  Earlier we found the force om q is North due to i1.  Therefore, the force on q due to i2 will be South.  If i1 > i2, then force due North will be greater than force due South.  The net force will be due North.

Try YouTube videos if the application of the right hand rule is not clear.  Videos can explain much better than writing could in this context.