Question

Which cause is used : formation of image of a person on a photographic film.

Answer 1

Photographic film captures the image formed by light reflecting from the surface being photographed. The sensitive elements in the film are crystals of, most often, silver halide which can change their structure when excited by light (photons). In general less sensitive films (slower films) have finer grains that are closely packed and more sensitive films (faster films) have courser grains. A film may have a distribution of grain sizes to obtain certain desirable properties. The reason for the sensitivity relationship to grain size is related directly to how the grains are converted from a stable non-developable state to another stable state (latent state) from which they can be developed chemically. This happens in something like the following way. When a photon of light strikes a grain it dissipates its energy in the crystal (grain). This energy may or may not be enough to flip the crystal into a latent state. Generally it takes a few photons to flip the grain (depending on its size and sensitivity). In the meantime, thermal energy is jiggling the grain and tending to drop it back into its normal state. If enough photons strike the grain in a given time, the grain flips to a latent state and sticks there. We then have a grain that can be turned opaque chemically. Thus the photons build up a latent image that is later developed. The darkness of the image is more or less proportional to the light striking the film. It takes about the same number of photons to flip a large grain as a small one. Since the larger grain intercepts more light more of the larger grains will be flipped and thus less light is required to create a latent image. This later phenomenon makes coarse grained films faster (more sensitive). All the silver halide salt particles reside in some emulsion layer depositing on the base layer of films. Color film has three layers of emulsion for three kind of silver halide which are sensitive for the light of 3 different light wavelengths. The following diagram shows the basic layered structure of photographic film.....

#ANONYMOUS....☺❤