# Homework Help: At what distance from the conductor is the magnitude of the resulting magnetic field

1. Jul 3, 2009

### mba444

1. The problem statement, all variables and given/known data
A long, thin conductor carries a current of
8.93 A.
At what distance from the conductor is
the magnitude of the resulting magnetic field
4.79 × 10−5 T? Answer in units of cm.

2. Relevant equations

B= Uo*I*l/(2*pi*d)

3. The attempt at a solution

i used this equation to figure out the distance but i keep getting the wrong answer
can someone explain wats going wrong ?!!

thanx

2. Jul 3, 2009

### Hootenanny

Staff Emeritus
Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

What is the l in your equation?

3. Jul 3, 2009

### mba444

Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

its the length

4. Jul 3, 2009

### Hootenanny

Staff Emeritus
Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

Well, the formula is incorrect, which probably explains why you've been getting the wrong answer. How did you arrive at that particular formula?

As an aside, what have you been using for the length of the wire since the question does not specify how long the conductor is?

5. Jul 3, 2009

### mba444

Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

Oops

i mixed up the parallel conducters equation with the straight wire equation

therefore is this the one B=Uo*i/2*pi*d

6. Jul 3, 2009

### Hootenanny

Staff Emeritus
Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

That looks good to me.

7. Jul 3, 2009

### mba444

Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

d=(4*pi*10^-7*8.93)/(2*pi*4.79*10^-5)= 0.011869 this is in meters so i converted it into cm i got 1.1869

8. Jul 3, 2009

### Hootenanny

Staff Emeritus
Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

I'd recheck your arithmetic and make sure that you are punching the numbers into your calculator correctly.

9. Jul 3, 2009

### mba444

Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

i did checked it again but still the same answer

10. Jul 3, 2009

### Hootenanny

Staff Emeritus
Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

Well using your numbers I get a different answer. You must be punching the numbers into your calculator incorrectly.

11. Jul 3, 2009

### mba444

Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

oka i got 13.0501 cm after correct my calculation but still the answer is wrong !!

12. Jul 4, 2009

### Hootenanny

Staff Emeritus
Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

Still not the same answer as I get. All I can suggest is that you check the manual that came with your calculator to ensure that you are entering the numbers correctly.

13. Jul 4, 2009

### mba444

Re: At what distance from the conductor is the magnitude of the resulting magnetic fi

i figured out my mistake thanx for your help