When the sum of the radii and the distance between the centres are equal, the circles touch externally. If the difference between the radii and the distance between the centres are equal, then the circles touch internally.
Xerography : is a photographic process which uses an electrically charged metal plate. On exposure to light the electrical charge is destroyed, leaving a latent image in which shadows are represented by charged areas. A powdered pigment dusted over the plate is attracted to the charged areas, producing a visible image.
Deoxyribonucleic Acid [DNA]
Deoxyribonucleic acid is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. DNA and RNA are nucleic acids; alongside proteins, they compose the three major macromolecules essential for all known forms of life.