Presentation on theme: "CAPACITORS…..What are they used for? Capacitors are components that are used to store an electrical charge. in timer circuits. added to a resistor to produce."— Presentation transcript:
CAPACITORS…..What are they used for? Capacitors are components that are used to store an electrical charge. in timer circuits. added to a resistor to produce a timer. to smooth a current in a circuit as they can prevent false triggering of other components such as relays.
A capacitor is composed of…….. A capacitor is composed of two conductors separated by an insulating material called a DIELECTRIC. The dielectric can be paper, plastic film, ceramic, air or a vacuum. The plates can be aluminium discs, aluminium foil or a thin film of metal applied to opposite sides of a solid dielectric. The CONDUCTOR - DIELECTRIC - CONDUCTOR sandwich can be rolled into a cylinder or left flat
HOW DOES A CAPACITOR WORK ? When the circuit is switched on, the light dependent resistor emits light and the capacitor charges up. When the switch is turned off the LED stills emits a light for a few seconds because the electricity stored in the capacitor is slowly discharged. When it has fully discharged it's electricity the LED no longer emits light. If a resistor is introduced to the circuit the capacitor charges up more slowly but also discharges more slowly.
Electrolytic and Non-Electrolytic Capacitors Electrolytic capacitors are ‘polarised’ which means they have a positive and negative lead and must be positioned in a circuit the right way round (the positive lead must go to the positive side of the circuit). They also have a much higher capacitance than non- electrolytic capacitors. Non-electrolytic capacitors usually have a lower capacitance. They are not polarised (do not have a positive and negative lead) and can be placed anyway round in a circuit. They are normally used to smooth a current in a circuit. Notice the electrolytic capacitors above. They all have two polarised leads, in other words they have a positive and negative leg. This type of capacitor is used with ICs such as the 555 timer chip and it is the capacitors and resistors that determine the timing sequence.
+ - Types of Capacitors REMEMBER - there are polarised and non-polarised capacitors. Look for a positive and negative sign.