# Calculate the B field inside and outside a wire

1. Sep 23, 2013

### DODGEVIPER13

1. The problem statement, all variables and given/known data
A long, straight wire of radius a has current density J = J0e−β(α−ρ)uz where β is a
constant and ρ < α. Determine B inside and outside the wire.

2. Relevant equations
J=I/((pi)a^2)
B=(μIρ)/(2(pi)(a)^2)

3. The attempt at a solution
Here is what I did B=(μρ/2)J0e^(-β(alpha-ρ))

Last edited: Sep 23, 2013
2. Sep 26, 2013

### DODGEVIPER13

Is the problem confusing?

3. Sep 26, 2013

### darkxponent

Not at all. First find i by integrating J then find B. di = JdA

4. Sep 26, 2013

### DODGEVIPER13

So ∫J0e^-β(α-ρ) from 0 to a but what should I integrate with respect too?

5. Sep 26, 2013

### DODGEVIPER13

J=di/dA maybe?

6. Sep 26, 2013

### DODGEVIPER13

well since beta is constant and alpha is greater than rho then e^(-beta(alpha-rho)) whould go to 0 if I took the limit from 0 to infinty

7. Sep 26, 2013

### DODGEVIPER13

hmmm well I guess the problem does not consider time as it uses J0 which I assume stands for the intial value

8. Sep 26, 2013

### DODGEVIPER13

So my limit I idea is flawed then

9. Sep 27, 2013

### DODGEVIPER13

Anything else?