Lecture on the Telephone

Major objective of this lecture is to present on the Telephone. here briefly describe on printed circuit board of the telephone and Telecommunication Optical Fibres. When a ray of light bounces off a mirror , the angle going in equals the angle coming out. The line at right angles to the mirror is called the normal. Optical fibres are made of thin flexible glass threads. They are about the size of a human hair. The fibres have a protective coating which keeps the light inside the fibre.