Capacitors are like batteries and sandwiches.
Definition: Capacitors are containers that save energy, just like batteries. Once a capacitor gets charged, it can replace a battery in a circuit for a short period of time. But most capacitors quickly run out of stored energy unlike batteries, they be charged again very quickly and reused. In the aspect of Composition, capacitor like a sandwich that consists of: two electricity- conducting plates with an insulator in between. The insulator can be anything that does not conduct electricity, but most commonly used are paper, glass, rubber, ceramic, and plastic. The conducting plates can be any metal that lets electricity flow easily, for example, aluminum, tantalum, and silver. General speaking, the smaller the distance between the metal plates, the larger the capacitor and the more energy it can store.
Then what is "parasitic capacitor"? The parasitic capacitor itself is not a capacitor. According to the definition of the capacitor, we can know that the capacitor is composed of two plates and an insulating medium, and the parasitic capacitor is not like that. For example, a circuit has many wires, and the capacitance formed between wires and wires is called parasitic capacitor. Parasitic capacitor generally refers to the capacitance characteristics exhibited by inductors, resistors, and chip pins at high frequencies. Parasitic capacitance generally affects the circuit in high-frequency circuits, so the circuit should be specially considered when wiring.
Harm: A capacitor itself is no a danger at all. It would be dangerous when charged because of the energy stored in them. During direct contact, at low energy, a capacitor can give someone a electric shock. At high energy for larger capacitors such as those used in heavy duty appliances like furnaces or in power systems, it can make a person unconscious or be potentially fatal. Discharging a capacitor is more dangerous than charging them. If discharging is not done safely, a charged capacitor, even one from a device as small as a camera flash, can kill a human being
Recycle: As time goes by, capacitor would develop higher internal resistance and lose their ability to store energy and the leakage current in between the metallic plates increases, which allows the current to flow through the insulator between capacitor plates and defeating the intended operation of the capacitor. A useful life of a capacitor is about 700 hours. Though e-waste recycling centers recycle this kind of electronic components, small capacitors are usually disposed of as ordinary waste. Oil filled capacitors contain PCBs (polychlorinated biphenyls) which are toxic and should be treated as hazardous waste.
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