Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Like direct current, alternating current is hindered by the resistance of the conductor through which it passes. In addition, however, various effects produced by the alternating current itself hinder the alternating current. These effects depend on the frequency of the current and on the design of the circuit, and together they are called reactance. The total hindering effect on an alternating current is called impedance. It is equal to the resistance plus the reactance.

The relationship of effective current, effective voltage, and impedance is expressed by V = IZ, where V is the effective voltage in volts, I is the effective current in amperes (amp), and Z is the impedance in ohms.