posted by Matteo .
Assume the Earth's magnetic field is 51.3 µT northward at 60.0° below the horizontal in a particular city. A tube in a neon sign stretches between two diagonally opposite corners of a shop window—which lies in a north–south vertical plane—and carries current 35.7 mA. The current enters the tube at the bottom south corner of the shop's window. It exits at the opposite corner, which is 1.39 m farther north and 0.850 m higher up. Between these two points, the glowing tube spells out DONUTS. Determine the total vector magnetic force on the tube. Hint: Two very important general statements are as follows. First, the force on the curved portion is the same in magnitude as the force on a straight wire between the same two points. In general, the magnetic force on a curved current-carrying wire in a uniform magnetic field is equal to that on a straight wire connecting the endpoints and carrying the same current. Furthermore, 1 + 2 = 0 is also a general result: the net magnetic force acting on any closed current loop in a uniform magnetic field is zero. (Take east to be the +x-axis, up to be the +y-axis, and south to be the +z-axis.)