The voice coil in your stereo speaker's woofer has 950 tight circular turns (in the plane), a diameter of 5.4 cm, and a coil resistance of 6.8 omega The stereo amplifier sends in a signal current into the woofer (voice coil) at a specific point in time such that the potential difference across the coil's leads is 1.8 volts. Determine the magnitude (in mT) of the magnetic field B, at the center of the voice coil.