# Magnetic fields/ force on conductors

1. Sep 1, 2008

### alice emily

1. The problem statement, all variables and given/known data
calculate a value for B at a distance of 50cm, in ,air, from a long straight cable carrying a current of 1000A.

2. Relevant equations
F=Bqv=BIl
I=q\t = qv/l
F=LIB

3. The attempt at a solution
i have not been able to calculate an answer as there are constantly two unknowns and i am unable o fine F.

2. Sep 1, 2008

### alice emily

i believe the answer is 4 x 10 to the -4 telsa

3. Sep 1, 2008

### johnj7

You're being asked to find magnetic field and not force due to the magnetic field, right?

The equations you wrote allow you to find the force due to a magnetic field, once you already know what B is. However, right now you're trying to find B due to the current. You need a different equation, that's hopefully in your book that relates B and current I.

4. Sep 1, 2008

### Defennder

yeah johnj7 is right. You need the proper equation. Look in your textbook for an equation relating B to a current carrying wire. Check online as well. If you're desperate and have learnt what is known as the Biot-Savart law, you can derive B from there.