Electronics is the study and application of electrons, their behaviour and their effects. The simplest application for electrons are straightforward AC and DC circuit in which a current is used to power lamps, electromagnets, motors, solenoids and similar devices. What takes electronics far beyond these basic applications is the ease with which streams of electrons can be controlled and manipulated.
This simple circuit is really useful bacause it can send information by converting a planned sequence of switch closures into flash of light.
Patterns of flashes or pulses like these can represent complex information like speech. Or speech can be transformed into proportional variation in the brightness of a lamp. Here's a simple way to send voise over a beam of reflected light:
A pulse is a sudden, brief increase or decrease in a current flow. The ideal pulse would have an instantaneous rise and fall, but real pulses are not so ideal.
A wave is a periodic fluctuation in a current or voltage. Waves may have a single polarity (DC) or both positive or negative components (AC). There are many kinds of waves. Here are a few:
A signal is a periodic waveform that conveys information. The process that generates the waveform is called modulation. Signal can be AC, DC or AC riding on a DC level. Their enemy is . . .
All electronic devices and circuit generates small, random electrical currents. When these currents are unwanted, they're called noise. Noise can also enter electronics circuits by means of the electromagnetic waves generated by lightning, automobile ignition systems, electric motors and power lines. While noise may have a level of only a few millionths of a volt or ampere, it may easily abscure an equally low level signal.