Direct & Alternating Current
Current in a circuit can be broadly divided into two categories: First, Direct Current which is current flowing in only one direction: Second, Alternating Current which periodically switches direction.
The term “passive component” refers to components that do not add power to a circuit. Resistors, capacitors, inductors, transformers, and even diodes are all examples of passive components. An active component is a device that has the ability to amplify a signal or produce a power gain. transistors, vacuum tubes, silicon-controlled rectifiers are some examples of active electronic components.
Resistors are passive devices that are used to limit current in both Alternating Current and Direct Current circuits. They are made of various resistive materials such as carbon composition or metal film. Resistors are designed to have specific resistant values from less than ohm to millions of ohms. Voltage is developed across a resistor as current flows through it. Power is dissipated in the form of heat as a function of the product of the voltage and current. The three major specifications of resistors are resistance value, tolerance, and power rating. Resistance value is pretty much self-explanatory. Tolerance indicates how close the actual resistance value is to the rated value.(1%,2%,5%,10%,20%) The power rating tells how much power the device can handle before overheating will cause damage.
Fixed resistors, Potentiometers, Rheostats, and specialty resistors are the major classifications of resistors. The symbols are shown for some of these are shown below.
A schematic diagram shows the electrical connections between components in a circuit. Each type of component is assigned a standard letter or letters called a “Reference Designator”. Resistors have a Reference Designator of “R”. The numbers associated with the R are assigned top to bottom left to right. The resistor numbers in the schematic links to the physical components in the actual circuit. The complete designation for a resistor in a schematic diagram includes the reference designator and the resistance value.
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