# Calculating B

1. Jul 5, 2008

### pooka

What is the magnetic field at the center of a 60-turn coil carrying a current of 4 A, if it has a radius of 0.2 m?

I was thinking of using the equation B=(mu0)(N/l)(current)

But I was wondering do I use the radius for l or do I use the diameter?

2. Jul 5, 2008

### rock.freak667

I think you need to consider it as flat circular coil instead of a solenoid

$$B=\frac{\mu_0 NI}{2r}$$

3. Jul 5, 2008

thanks!