# Magnetic Field of A Solenoid.

1. May 5, 2017

### Arman777

1. The problem statement, all variables and given/known data
A 470-turn solenoid having a length of 25cm and a diameter of 10cm carries current of 0.29A. Calculate the magnitude of the magnetic field inside the solenoid.

2. Relevant equations
$B=μ_0nI$
where $n=\frac N L$
$μ_0=4π.10^{-7}\frac {Tm} {A}$
$n=\frac {470} {0.25m}=1880\frac 1 m$

3. The attempt at a solution
$B=μ_0nI$
$B=4π.10^{-7}\frac {Tm} {A} 1880\frac 1 m 0.29A$
It gives me $0.68mT$ but answer says its $0.71mT$

I didnt understand where I am doing wrong.Question also gives us the diameter but I dont know where to use it.

2. May 5, 2017

### Staff: Mentor

Your calculations look okay to me.

Someone may have changed the problem a bit (to make it a "new" problem) but forgot to update the answer key. I note that had the current been 0.30 A rather than 0.29 A that their answer would be correct.

3. May 5, 2017

### Arman777

Probably yeah thanks