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.


Rectification (electricity), process of converting an alternating current (AC), which flows back and forth in a circuit, to direct current (DC), which flows only in one direction. A device known as a rectifier, which permits current to pass in only one direction, effectively blocking its flow in the other direction, is inserted into the circuit for the purpose.

Rectification is carried out at all levels of electrical power, from a thousandth of a watt to detect an AM radio signal, to thousands of kilowatts to operate heavy electrical machinery. The first commercial rectifiers were used in the conversion of alternating to direct current in the operation of electrical motors; these early rectifiers were called mechanical commutators. Today, most rectification is carried out by electronic devices, such as combinations of vacuum-tube diodes, and mercury-arc rectifiers.

Most mechanical rectifiers consist of a rotary switch that is synchronized with the current; the switch is arranged to conduct the current in one direction only. Mechanical rectifiers can be designed and constructed to handle heavy currents (up to thousands of amperes) at levels of several thousand volts, and they are still used in heavy electrical machinery.

Electronic rectifiers conduct current in one direction only by the motion of electrical charges inside the device; they can carry currents as high as 500 amp and withstand voltages up to 1000 V without damage. These rectifiers, therefore, can compete with mechanical rectifiers in many power applications. In low-voltage applications, such as in electronic equipment, either vacuum-tube or semiconductor rectifiers are used almost exclusively.