A(n)
reverses the flow of current through an electric motor.

Commutator is a ring which reverse the direction of current in AC circuit so that the coil connected to it will continuous to move in the same direction.

Explanation:

In motors there exist a coil which is rotated due to torque of magnetic field when current flow through it. Since AC current is used to run the motor so we know that AC current changes its direction after half cycle.

So here commutator plays an important role to reverse the direction of current after every half cycle so that the current goes in same direction always into the coil.

This will produce a constant direction torque on the coil so that it will rotate in same sense always.

So commutator role is to provide same direction current to the coil by reversing its direction after every half cycle

a.) travels faster in solids because the particles are closer together.

air is a gas water is a liquid

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.