A capacitor is an electrical component which different functions consist in receiving, storing, stabilising and releasing an electrical charge. Several capacitors exist. The most simple form consists in two face-to-face plates (electrical conductors) separated by an isolation material also called dielectric.
The choice of the insulation material is essential since it determines the tension above which a breakdown current may appear which would lead to the capacitor’s total destruction.
A printed
circuit is a single or multi-layer socket which function consists in gathering
a certain number of electrical components in order to obtain a circuit. This
socket (electronic circuit) is made of an insulation layer on which conductive tracks
are displayed.
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Relays
A relay is an electrical device which is mainly composed of an electromagnet. It controls on a remote way the switch on/off of a mechanical or electronical device. The relay, being disconnected from the circuit, is insulating both systems but also the current amplification.
Applications 
Capacitors
Printed circuits
Relays
MICEL Electro INFO