Technician: Switch Components

Which of these components can be used as an electronic switch or amplifier? [T6B03]

A. Oscillator
B. Potentiometer
C. Transistor
D. Voltmeter

Piece of cake this one is….  Lets go through the false answers first, just to make sure.

A. Oscillator.  By definition, an oscillator simply takes a signal and, well, oscillates it.  on/off, high/low, whatever.  While definitely important in radio (you can’t get an alternating waveform without one) you can’t really make a switch out of one.  It is possible to use an oscillator as an amplifier.  It’s how vacuum tube radios get the work done (and that’s our first clue!)

B. Potentiometer.  A potentiometer is nothing more than an adjustable value resistor.  While it may have a switch built into it, such as an on/off/volume switch combination, a potentiometer by itself doesn’t make a particularly good switch.  I suppose you could use it as one, by increasing a signal via the “pot” up to or below a given “cutoff” value…. but that’s a bit of a stretch.

D. Voltmeter.  A voltmeter simply measures the voltage across a given circuit or component.  Nothing more.  It’s quite impossible to use one as a switch.  (I think!)

So all that remains is C. Transistor.  A transistor is a solid state device that toggles between states depending on an external input.  By placing (for example) a 5V load on a transistor you can essentially “flip the switch,” and removing the voltage will turn it off again.


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