A student makes a short electromagnet by winding 480 turns of wire around a wooden cylinder of diameter d = 4.9 cm. The coil is connected to a battery producing a current of 4.2 A in the wire. (a) What is the magnitude of the magnetic dipole moment of this device? (b) At what axial distance z >> d will the magnetic field have the magnitude 4.4 µT (approximately one-tenth that of Earth's magnetic field)?

A student makes a short electromagnet by winding 480 turns of wire around a wooden cylinder of diameter d = 4.9 cm. The coil is connected to a battery producing a current of 4.2 A in the wire. (a) What is the magnitude of the magnetic dipole moment of this device? (b) At what axial distance z >> d will the magnetic field have the magnitude 4.4 µT (approximately one-tenth that of Earth's magnetic field)?