# B field

1. Sep 30, 2008

### MIA6

1.Two long, straight, parallel conductors carry equal currents and are spaced 1.0 meter apart. If the current in each conductor is doubled, the magnitude o the magnetic force acting between the conductors will be 1)Doubled 4) quadrupled.
I chose 2 because I used the formula is F=ILB, so if I is doubled, then 2F=2ILB, F doubled as well, but the answer was 4), I didn’t use d=1 in that formula, so is there any other formula which includes d between two conductors?

2. Assume the magnetic field produced by the magnet and the electric field produced by plates X and Y remain constant. If the potential difference between the filament and the plate is increased, the force of the magnetic field on the electrons will
1) increase 2) decrease or 3) remain the same
I don’t understand why potential difference V matters the force? And what does it mean by filament?

2. Oct 1, 2008

### alphysicist

Hi MIA6,

Call them wire 1 and wire 2. You are looking at the force on wire 1, and the I in that equation is the current of wire 1. What does B in that formula represent? and is there another formula for it?

(There are other ways to get this answer, but your approach will work fine.)

3. Oct 1, 2008

### MIA6

But my approach was wrong in this case. It's supposed to quadruple, but mine doubled.

4. Oct 1, 2008

### alphysicist

No, your approach will work, you just did not figure in all the changes. Your equation is:

$$F=ILB$$

so you saw that I will double and L will stay the same. But what happens to B? It does not stay the same, and so my question was what is B? What is creating it in this case, and what other equation describes it?