In electronics, an active component is one that has gain or depends on the direction of the current. In practice, this means any component that is not a resistor, capacitor or inductor (which are termed passive components). Examples of active components are transistors, thyristors, diodes and valves. Two digital voltmeters The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The word current usually implies a flow or movement. ... Resistor symbols A resistor is a two-terminal electrical or electronic component that passes a current that is proportional to the potential difference between its terminals in accordance with Ohms law. ... Various types of capacitors A capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. ... // Definition An inductor is a passive electrical device that stores energy in a magnetic field, typically by combining the effects of many loops of electric current. ... A passive component is an electronic component that does not require a source of energy to perform its intended function. ... High-power transistors used in a switching power supply. ... Circuit symbol for a thyristor The thypissor is a solid-state semiconductor device similar to a diode, with an extra terminal which is used to turn it on. ... Types of diodes A diode can be thought of as the electronic version of a one-way valve. ... A valve is a mechanical device that regulates the flow of fluids (either gases, fluidised solids, slurries or liquids) by opening, closing, or partially obstructing various passageways. ...

• Think, for example, of a book on your desk. It is not connected to anything that will cause an electric current to increase, nor decrease. It is not "active".
• Think of the telephone on your desk. It is connected to something "outside" that will let a current flow and change, and let you talk to many people in many places on this planet, if nessessary. It is "active" although it may not be doing anything at the present time.
• Think of a smoke detector on the ceiling. It has a battery in it that can do something, if necessary. A smoke detector is therefore "active".
• Think of a sound amplifier. It has "gain", meaning it makes stronger whatever is sent to it as an "input". It is "active".
• Electric/electronic equipment, such as a TV set, or a computer, or a calculator, has many components in them, active components included.