# Homework Help: Force of one wire due to the other

1. Jun 20, 2013

### aChordate

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

D=1.0cm=0.01m
I=1.0A

2. Relevant equations
B=(μ0I)/(2∏r)

3. The attempt at a solution

B1=(4∏x10^-7 * 1.0A)/(2∏ * 0.01m)= 2.0x10^-5

B2=(4∏x10^-7 * 1.0A)/(2∏ * 0.01m)= 2.0x10^-5

Not sure what to do with these two numbers.

2. Jun 20, 2013

### barryj

How does the force on a wire relate to the current through the wire and the B field?

3. Jun 20, 2013

### aChordate

I would use the Right Hand Rule to find the relation. Since the current is going upward (thumb), the magnetic field B would be going into the page (fingers) and the force would be pointing to the left (direction the palm faces).

4. Jun 20, 2013

### barryj

The right hand rule will give the direction of the force but not the magnitude. You have found B, the magnetic field produced by a wire carying 1 amp at a distance of 10 cm. Now How do you find the magnitude of the force on the wire that is in this field?

5. Jun 20, 2013

### aChordate

Would I use F=|q0|vBsinθ ?

6. Jun 20, 2013

### aChordate

Wait, nevermind. That would be for a moving particle.

7. Jun 20, 2013

### barryj

F = BIL, remember this?

8. Jun 20, 2013

### aChordate

F=ILBsinθ would be the equation, I think.

9. Jun 20, 2013

### aChordate

Oh, saw your post after I posted. Oops. What would be L? I thought that L was the length of the wire, but that was not a given variable.

10. Jun 20, 2013

### darkxponent

If you have studied Vectors i would suggest you use the more general equation force that is i*L(cross)B

11. Jun 20, 2013

### barryj

F=ILBsinθ is technically correct and is used if the wire is not perpendicular to the B field which it is in this case. s far as what is L, look it up in your text. It will do you some good :-) Remember the force requested is per unit length.

12. Jun 20, 2013

### aChordate

Oh ok, so...

F/L=(1.0A)(2x10^-5)

and sin90=1

So F/L=2*10^-5

13. Jun 20, 2013

### aChordate

would the units be Gauss/meter?

14. Jun 20, 2013

### barryj

What is the unit of force?

15. Jun 20, 2013

### aChordate

oops, N/m!!

16. Jun 20, 2013

### barryj

Remember that this is a two step process. Step 1 is to determine the B
field in the vicinity of the wire, and step 2 is to determine the force on the wire due to the B field generated by the other wire..