Could someone explain the wording (and possibly see if I'm going the right way about it) of this question to me. What is the current required in the windings of a long solenoid that has 1000 turns uniformly distributed over a length of 0.400m, o produce at the centre of the solenoid a magnetic field of magnitude 0.1mT. The wording I'm concerned about is about the turns. Is the wire 40cm long with 1000 turns, or is each turn 40cm long? Anyway to the working: I thought initially to use F=nBIl, but as no force is given I can't use it can I? Is it something to with Biot-Savart's law? I want to use the form, B= NI(mew0)/2a, but I can't think how to find a, the distance to the center of the circular loop. Any hints?