قوس الكربون الكهربي .. كتاب الإضاءة والفلم

CARBON ARC.

When two conductors connected to the poles of an electrical source come into contact and then separate from each other, a spark occurs between them, which is called the “arc.” The spark continues to occur as long as the distance between them is short. This always happens regardless of the type of material the poles are made of. However, if they were made of any metal, the heat would affect them and they would melt quickly at both ends. Hence, the validity of using carbon in the two poles of the electric arc appeared, as carbon does not melt when the temperature of its two sides rises to a high degree, but rather turns into gas directly without passing through the liquidity stage. For this reason, we find that during the action of the carbon arc, each of its ends is ignited as a result of ignition. If the poles are far apart from each other, the electric arc will not be regular, so work must be done to gradually approach the distance between its poles in a proportion equal to the proportion of atoms consumed by combustion. And when the two ends of the poles touch and then separate, the burning gases that make up the spark act as a conductor with high resistance to the electric current, as they play a role similar to what the incandescent tungsten filament does in the regular Incandesecnt Tungsten Filament, and therefore this gaseous conductor emits light, in addition to the lighting resulting from the surface carbon in contact with it, and they emit large light energy. The material from which the poles are made may be pure carbon, or may be deliberately mixed with some mineral salts.

Carbon arcs differ from each other in terms of the following properties and characteristics:

A - for lighting contrast

(a) There are types of electric carbon arcs that emit light rays characterized by high contrast, hard lighting, without a gradation in the intensity of light between the lighted areas and the shadows areas, i.e. their rays are sharply defined.

Therefore, such sources become suitable for illumination in devices that operate on an optical basis (ie, that carry lenses) such as projectors or in focused light devices.

(B) And other types that are not distinguished by this strong contrast and are suitable for lighting assets in Photographic Reproduction operations.

2- Regarding the type of electric current:

Some of them work with a continuous electric current. D. C (ie Direct current), and the other works. An alternating electric current A.C, which is sometimes known as Alternative current Enclosed.

3- With regard to whether it is covered with glass or not:

(a) Some types are coated with glass

(B) and other types that are open and exposed to the air.

4- With regard to the purity of carbon or its mixing with impurities:

(a) Some types have pure carbon that is not mixed with Plain Carbon impurities and is not fed by a strong electric current, so it does not lead to very strong lighting and is known as

(b) And others in which carbon is deliberately mixed with mineral salts and a strong electric current is conducted in them, which leads to very bright lighting known as

5- With regard to the color temperature of the rays and their suitability for color photography:

(a) Some of them emit rays with a low color temperature, close to the color of the rays of tungsten lamps.

(b) The other emits rays whose color temperature is higher than the above and is consistent with the color of daylight rays. We will discuss the following in the previous types.

An open carbon arc with a low optical density

Low intensity open arc.

Once DC power is connected.D. C with the two poles of carbon, the positive pole begins to erode from its center at the point where the spark connects, forming a conical gap.

1- Since the center of light emission is usually located in this conical crater, therefore the positive pole is made of less solid carbon than the one from which the negative pole is made, thus facilitating the occurrence of this crater.

2- In order for there to be a proportionality between the duration of consumption of the two electrodes, the positive electrode is made of a larger diameter than the negative one.

3- When the electric arc is a light source in an optical device (such as a projector or a spot light source), it is taken into account that the positive pole is in a suitable location in front of the capacitor, so that it is able to emit the largest light energy, noting that the negative pole is not an obstacle to The conical nozzle at the positive pole (which emits most of the light energy).

The following are wrong with this type of electric arcs:

(a) The low light energy it emits (which is why it is called Low (Intensity Arc).

(b) The low color temperature of the rays it emits (from 2700 to 3000 K), i.e. it is close in color to the color of the rays of tungsten lamps.

Therefore, manufacturers tried to overcome the previous defects by making the electric arc covered with glass, known as Enclosed Are.