Magnetism - Quick solenoid question

[thehammer]

Homework Statement

A 200-turn solenoid having a length of 25cm and a diameter of 10cm carries a current of 0.29A. Calculate the magnitude of the magnetic field B inside the solenoid.

Homework Equations

B = $$\mu$$₀ni

The Attempt at a Solution

Well, I plugged the numbers into the equation and got 7.28x10^-5 T as the answer. However, this is wrong. The correct answer is meant to be 0.3 mT. I can't see where I've gone wrong because the magnetic field inside a solenoid is meant to be independent of its dimensions, right?

EDIT: I found the number of turns per unit length, then put that into the equation and still get the wrong answer. I'm confused.

B = 4$$\pi$$x10-7 Tm/A x (200/0.25) x 7.5A = 7.28x10^-5.

I've no idea why I get that. Maybe the diameter has some significance that I haven't managed to see yet.

 

[Doc Al]

Show exactly what you plugged in for each factor.

 

[Doc Al]

A 200-turn solenoid having a length of 25cm and a diameter of 10cm carries a current of 0.29A.

...

B = 4$$\pi$$x10-7 Tm/A x (200/0.25) x 7.5A = 7.28x10^-5.

Looks to me like you are using the wrong current.

 

[thehammer]

Oops. I apologise for wasting time. I used a current from a different question by accident :).