What causes the poles of the electromagnet in an audio speaker to repeatedly switch directions? a metal striker that pulls on the magnet
a diaphragm that vibrates around the magnet
a current that rapidly switches direction
a device that opens and closes a circuit

C. A current that rapidly switches direction.

Explanation:

no sign of dia of fuel cell

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.