How The Crystal Oscillator Starts Oscillating..

Quartz crystal oscillator that we use in micro-controller lab oscillates giving constant frequency.Have u thought how does it starts oscillating.

As far as I know ,a crystal of quartz is properly cut and mounted so that it can be made to distort in an electric field by applying a voltage to an electrode near or on the crystal.This property is known as piezoelectricity.This means we apply certain voltage at starting  and than after due to piezoelectric effect it continue oscillating.  When the field is removed, the quartz will generate an electric field as it returns to its previous shape, and this can generate a voltage. 

It means, pin of micro-controller at first supply voltage..what do u think??

Different Types Of Capacitor at Different Place In Circuit

   I always used to think when I saw capacitor used in circuit ,"Why electrolytic capacitor is used here not ceramic or paper etc.??what is there working difference??what will happen when I use ceramic instead of electrolytic??". I started querying about it with teacher ,seniors and by my own surfing i got one perfect reason behind it , that is..

Several solid dielectrics are available, including paper, plastic, glass, mica and ceramic materials. 

1. Paper was used extensively in older devices and offers relatively high voltage performance. However, it is susceptible to water absorption, and has been largely replaced by plastic film capacitors.
2. Plastics offer better stability and aging performance, which makes them useful in timer circuits, although they may be limited to low operating temperatures and frequencies.
3. Ceramic capacitors are generally small, cheap and useful for high frequency applications, although their capacitance varies strongly with voltage and they age poorly. 
4. Glass and mica capacitors are extremely reliable, stable and tolerant to high temperatures and voltages, but are too expensive for most mainstream applications.
5. Electrolytic capacitors and supercapacitors are used to store small and larger amounts of energy, respectively with maximum operating voltage.If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 
 

If any body have certain comment's regarding it..than please forward it,,