الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Lectures in General Physics
inexpensive to make these images because the photoconductive insulating
layer can be recycled many thousand times. The process has found its
primary usefulness in copying office documents and in low-volume
duplication of data.
(a) The photoconductive surface is positively charged. (b) Using a light source and lens, an
image is formed in the surface in the form of hidden positive charges. (c) The surface
containing the image with a charged powder, which adheres only to the image area. (d) A
piece of paper is placed over the surface. This transfer the visible image to the paper,
which is heated to ix the powder to the paper.
The xerographic method also permits the making, quickly and cheaply; of
paper offset masterplates for low-to-medium-volume runs on office offsetprinting
presses. The method has also been applied to the production of X-
ray images in a technique that is known as xeroradiography and is used in
mammography for early detection of breast cancer. Xerography is applied in
industrial nondestructive testing.
A variety of automatic xerographic machines are available today that make
office copies on the push of a button and that are almost unable to fail.
Xerographic machines can reproduce half-tone photographs and can enlarge
or reduce copy. They can be set to print on either one or both sides of paper,
to produce automatically a large or small number of copies without further
intervention by the operator, and to sort and collate. A development of the
late 1970s is color xerography. The economy, versatility, and flexibility of
the xerographic process have created legal problems relating to copyright
and helped stimulate numerous changes in the copyright laws in the U.S.
and elsewhere.
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Dr. Hazem Falah Sakeek 237