Question

A loudspeaker creates sound by pushing air back and forth with a paper cone that is driven by a magnetic force on a wire coil at the base of the cone. (Figure 1) shows the details. The cone is attached to a coil of wire that sits in the gap between the poles of a circular magnet. The 0.20 T magnetic field, which points radially outward from N to S, exerts a force on a current in the wire, moving the cone. The coil of wire that sits in this gap has a diameter of 5.0 cm, contains 20 turns of wire, and has a resistance of 8.0 Ω. The speaker is connected to an amplifier whose instantaneous output voltage of 8.0 V creates a clockwise current in the coil as seen from above. What is the magnetic force on the coil at this instant?

Answer 1