Showmen's Trade Review (Oct-Dec 1944)

October 7. 1944 SHOWMEN'S TRADE REVIEW 41 100 E R R R= — . I — '■ — w w W Here are a few problems in arithmetic as it IS APPLIED TO Ohm's Law. R EQUALS OR means the restance in Ohms. I means the intensity of the current or the amperage. w means the wattage of the device or circuit or the ENERGY CONSUMED OR PRODUCED. * The sow for each lamp in diagram above indicates size of the lamp and not the wattage being consumed. The value of wattage as referred to in text below is the value actually being consumed. to establish an electrical circuit. We hold the carbons in contact for an instant (which permits the carbons to become incandescent) and then we separate them slightly. The instant we do so a small spark occurs which causes some very tiny particles of the carbon to burst into flames in combination with the air which surrounds the carbons. This flame becomes a volitalized area which will conduct electrical current. The continuous flow of current through the arc further heats the carbon and combustion is maintained and a steady arc results. By mixing certain chemicals and depositing the mixture in the center of the carbon rods we can increase the brilliancy of the arc and this is the general practice today. The same rule as to the amount of current that can be economically conducted applies to carbon as to copper except that carbon decreases its resistance as the temperature increases. So if we wish to increase the brilliancy of our arc by increasing the' value of current flow we will have to increase the diameter of the carbon proportionately. (Notice that the length of the carbon rod does not affect the amount of light or the value of current flow. We always start off a reel of film with a relatively long piece of carbon and finish up with a rather shorter length of carbon and still the light on the screen does not change noticeably. It is the diameter of the carbon that is important.) There are certain set formulae that are used in determining the value of voltage, resistance, and current in an electrical circuit. The rules follow the following patterns : It will require one Volt to cause one Ampere to flow through a resistance of one Ohm. (That in a nut shell is the Law of a Direct Current Circuit.) By transposing the above we may solve for any one unknown whenever we have the other two. Volts divided by resistance will announce the current flow. Volts divided by the current will tell the resistance of the circuit. Resistance multiplied by the current will indicate the volts applied to the terminals of the circuit. Whenever voltage forces current through a resistance heat is produced and work is performed. The amount of energy used in performing this work is termed the Wattage of the circuit and may be determined by the product of the pressure and the speed of the movement of the electrons. Hence the voltage times the current will give the wattage of the circuit. Use a numerical value of ONE in the above divisions and multiplications and you will find that the answer is always ONE. Using a value of five for voltage and also for current you will find a resistance value of ONE and a wattage value of twenty-five. Use other values and practice these formulae and you will become quite proficient in the use of Ohm's Law for a direct current circuit. Now let us look at this resistance of a circuit jn another way as a means of establishing a foundation for explaining just how the association of more than one resistor in a circuit can and does affect the amount of current flowing in the circuit as a whole. Suppose we represent the wires of the circuit as a pipe that will conduct water from one point to another. The tank from which the water is flowing or is stored will be considered as the Electromotive Force that will force the water to go through the pipe. The smaller the diameter of the pipe the longer will be the time consumed before the tank becomes empty of water. We can now say that due to the small diameter of the pipe or THE RESISTANCE of the pipe the water will flow slowly through the pipe. If we were to increase the diameter of the pipe to twice its former diameter the water would flow just four times as fast — or in other words the larger diameter pipe offers just one-fourth the resistance as the smaller pipe. This holds true in wire. Now should we tap the tank so as to connect another pipe alongside the first, we then would permit the water to flow out through two egresses. Each one of these are equal. In this connection we will now have twice as much flow in both pipes as we had in one alone. We have now decreased the resistance of the pipe to one-half, since the flow is twice as great the restraint is halved. This is a very common situation in an electrical circuit especially when we have more than one electric light lamp that is operated from the same switch or the same two wires. Thus we can now see what happens as we connect more and more lamps in the same circuit. As the number of the lamps increase the total resistance of the circuit decreases and as the resistance decreases the current flow increases. Now we are concerned with the method of {Continued on Page 42) — WAGNER TRANSLUCENT PLASTIC CHANGEABLE LETTERS Hundreds are now using these attention compelling letters to attract business. By daylight they afford sharply silhouetted copy and by night the colorful brilliance of neon. They can be used outside on the marquee in Wagner frames, or inside in Wagner Lobby Displays. These, the only translucent plastic molded letters on the market, are strong, durable, last almost indefinitely, and permit fullest utilization of light, which shines through them. 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