Showmen's Trade Review (Oct-Dec 1944)

40 SHOWMEN'S TRADE REVIEW October 7, 1944 P«o.,ECT,os cLixK d/s^uSE and EFFECT of VOLTAGE DROP By Tom McNamara lATSE 505 It will be remembered that we previously referred to the action of the electrons making up the copper wire. Well, we will have a little more investigation to do before we can properly consider current flow completely. We spoke of the atom and broke it down into its protons (positive charges) and its Electrons (negative charges). All of the electrons do not participate in the job of conducting current. We may say that rotating around the nucleus of the atom are all of the electrons that are contained in the atom. This nucleus can be construed as all of the protons that make up the atom. The electrons rotate around the nucleus in their own orbits. It so happens that some electrons rotate in a rather smaller diameter than others. These closer electrons are very close to the center of the family, so to say, and are under the complete domination of the nucleus. The other electrons rotate around the nucleus all right but at a greater distance from it and are not so completely controlled by the nucleus. These we call the "free electrons," and they are our favorites for they work for us. Aware of the fact that only part of an atom cooperates with us we must recognize this as a limiting factor if we wish to conduct current in a wire without the production of heat. For if we attempt to force the bound electrons to work for us the atom protests. It will take extra work on our part to compel them to do our work, hence we will have to expend energy that could be saved by simply increasing the diameter of the wire to a point where we will have a sufficiency of Article IVo. 5 In Fundamentals Of Projection wire to do our work without the production of heat. This is our policy and now you know the reason for increasing the size of a wire when we have considerable current to conduct and you also know why the fire underwriters have something to say about the size of the wire, for if the production of heat goes far it is possible that a conflagration will result. Thus you can see that the refusal to do more than a certain amount of work at any one time does not originate with the human specie, and. this is the fearful part of technocracy. Since we have a certain percentage of electrons that are willing to do our work, we refer to this as the conductance of a certain size wire. Hence the conductance of a wire will increase as we increase the diameter of the wire. On the other hand since we have a certain refusal to do work we have the natural resistance of the wire, and this is so termed. So for a certain diameter wire we have the conductance or willingness of the wire to do work and the resistance or unwillingness to do work. The conductance of a wire is the reciprocal of the resistance or the resistance of a wire is the I TOMORROW'S PERFECT PROJECTION ORTHOSCOPE LENSES These New Lenses Will . . . 1. Definitely improve distribution of light on the screen ... No more dark edges 2. Eliminate the "hot spot" 3a Amazingly improve color projection 4 Do away with side and front seat distortion 5 Perfect background focus on longshot scenes 6. Give greater picture "depth" 7. Do away with "rainbow" effects 8 Cause film to run cooler ... no buckling ASK YOUR NATIONAL REPRESENTATIVE FOR DETAILS Distributed Exclusively by NATIONAL T H E A T R E S UP PLY Diviiion of National • SimpUx • I ludwor(h,ln<v reciprocal of the conductance. We can easily find the resistance of a piece of wire by using the figure of 10.35 ohms per mil foot as the specific resistance of the wire. There are other metals that have a higher resistance than copper and we find a great deal of use for this wire. In fact no electrical device could manage very well without resistances. Some people who do not know much about radio devices or amplifiers are prompted to ask what appears to be funny questions when they see the insides of the amplifier or radio receivers. They often ask "just what are the firecrackers used for." The resistors do look like old fashioned firecrackers. Resistances are used whenever we wish to create heat electrically such as in our soldering irons, our electric toasters and electric stoves and many other devices. Resistance is also used whenever we wish to create light — such as in our electric light bulbs, projection arc lamps and many other devices. Thus we see why the behavior of the electrons while under the influence of an electrical current is a very important study. We deliberately select certain kinds of metal for the production of heat because the electrons are reluctant to flow in the manner prescribed and when compelled to do so by the application of sufficient current the electrons will spin so fast that they produce considerable heat. This chosen metal has another desirable factor and that is its high melting point which preserves its form and shape even though we cause it to become partially incandescent while under the electrical influence. Hence a wire that has poor conduction or high resistance and at the same time has a high melting point is a very desirable type of wire to use whenever we wish to produce heat electrically. This wire also has another desirable characteristic, which is its ability to cause a voltage drop. Suppose we have a voltage source of ten volts and only six volts are required to do a certain job. By using a certain amount of this resistance wire we can cause a drop of four volts in the resistance wire and still have enough voltage to do our required job. Now suppose we wish to produce light electrically. Well we will use another piece of wire and subject it to the electrical influence. This wire will become incandescent to a minor degree when we force it to conduct current to a greater extent than which it is normally capable. The wire will get brighter and brighter until it will separate or melt at its weakest point and we will then have an open circuit. This breaking of the wire is due in part to the temperature of the wire combining with the air and a sort of combustion takes place at the weakest ' point of the wire. Then if we protect the wire against this combustion by placing the wire in a vacuum we will be able to vastly increase the brilliancy and prevent the breaking of the wire because of the absence of air which permits combustion to take place. Thus we have our electric lamp. The same conditions prevail in our carbon arc lamp in that we bring our carbons together