A capacitor can store a static charge. A Leyden jar was an early form of capacitor, charged by electrostatic means. The unit of capacitance is the farad.
Conductors may be in a parallel circuit or in a series circuit. At the junction of any circuit, all electric currents must obey Kirchhoff's laws.
Resistance is measured in ohms, conductance is measured in mhos, each refers to a conductor's capacity to allow electrons to pass through it.
A potentiometer (or a rheostat) has a variable resistance because a slider can tap in at various points on what is generally a uniform resistor.
A light dependent resistor can be used to measure light intensity, because the resistance it causes to a current is proportional to the light falling on it.
A light dependent resistor can be used to measure light intensity in a uniform way, since the resistance varies with the intensity of the incident light.
A reed switch uses a magnetic effect, changing from one state (with the switch open or closed) to the other when a magnet is moved near it or away from it.
An image intensifier is a device that allows us to see in what is effectively the dark, by taking the few available photons and amplifying them.
Electrons can flow through a vacuum, and this is the basis of the thermionic valve, where electrons are 'boiled off' a hot cathode and then travel to an anode.
Thomas Edison made just one real scientific discovery, the 'Edison effect', which is the key to the thermionic valve. He patented it, but never used it.
An integrated circuit or chip contains many separate semiconductor devices, all of them incorporated into a single unit, made in a single process.
Modern electronics relies on semiconductor devices: a diode only allows current to flow in one direction, a transistor can act as a switch or an amplifier.
The strength of a signal may be increased with an amplifier, a circuit designed for that purpose, and using either thermionic valves or transistors.
A diode only allows current to pass in one direction, and a set of diodes may be arranged to make a full-wave rectifier, as in a conventional power pack.
In 1947, the transistor effect was noted, and by 1948, William Shockley, Walter Brattain, and John Bardeen had made and proven the first working transistor.