Showmen's Trade Review (Oct-Dec 1944)

40 SHOWMEN'S TRADE REVIEW December 2, 1944 of CONDENSERS By Tom McNamara lATSE 505 What is a Condenser (or Capacitor) ? Any two conductors separated by a dielectric is a condenser. This is a very important definition even though it sounds simple. (The wires of an amplifier or radio set and the closeness of the elements within a vacuum tube itself are so close to each other that they constitute condensers and must be considered and compensated for when constructing tubes and amplifiers.) In order to understand the function of a condenser we should go back to the study of electrons. The electrons that make up our conductor wire are pursuing their own individual orbits whenever they are not subjected to any outside influence. However, the instant that we connect these wires to a voltage source the orbits of the electrons within the wire assume an orbit depending upon the polarity of the electrical source. That is to say, they rotate in one direction when the wire is connected to the positive pole and in the opposite direction when connected to the negative pole. Rule to Determine Current Flow You may have read about the "Right Hand Rule" for determining the direction of current flow. An adaptation of this rule may be used to illustrate the direction of electron flow as well as their rotation in a wire. Thus : grasp a piece of wire in your left hand (palm down and thumb extended to right along the wire), and now assume that the rotation of the electrons is in the direction indicated by the position of your fingers, and the direction of the electron flow, in the direction indicated by your thumb. The latter is known as electron drift. Thus it is seen that we have two movements of electrons — a rotation around a central axis and, simultaneously, a drift along the length of a wire. The drift of electrons is much slower than their rotation. Now, if we connect a loop of wire from one terminal of a battery to the other terminal we would have a short circuit. However, let us do this mentally just in order to follow the electrons around our external circuit. To do so we position the battery so that the negative terminal is on our left and the positive on the right hand side and our loop of wire will extend outward in front of us. Placing our left hand around the wire leading from the negative terminal we will illustrate that the direction of rotation and also that of the drift of electrons will approach the battery's positive terminal as the drift is completed in the circuit. Now we may say that the negative pole of the battery drives the electrons (which are negative charges) away from that pole and that the positive terminal of the battery attracts the electrons to it, thus agreeing with our original rule that "Like poles repel and Unlike poles attract." This ac'-ion would continue until all of the material within the battery that is used for the purpose of producing electrons is exhausted and our battery is then considered dead. As a further illustration, let us cut our loop of wire equi-distant from the two poles. We have now produced an open circuit and no current will flow through it. But what is the condition Article No. 7 In Fundamentals Of Projection Figure 1. 45 Vo\h Direciion of Electcoh Foil Plate POS ."+""^'fo". "PAPER I Plate Figure 2. Lea a ■/^///. Plate 1 / V Lead p/'^^*" \ . . ./ INDUCTIVE I raper as dielecTric TVOB and insulation TYPE FiriiJPO ^ Symbol -for Fi9ure +. Amount of Election Flow I I I I ' I I ■ I I I I I I I I I Time in Seconds Figure 4-a Voltage Condenser I I — I — I — I 1 — I — I — I 1 — I — I — I — I — I — 1 — 1 — \ Time in Seconds Figure 2-a -FoM 1. -Paper Symbols Variable trimmers CONDENSER ~]^otor « PAODERS CONNECTION of TRIMMERS PADDERS Trimmep Tuning^ -[/Tuning Padder in each wire connected to the poles of the battery? Touching the wires with a voltmeter at any point along the wire's length will indicate a voltage of the proper polarity. Therefore, there is an electrical presence in the wire. Since we can identify the polarity of the wires we can presume that the wires are charged. As there is a positive pole and a negative pole we have opposite poles and we also have a condenser. Placing these wires close together will cause an interaction between the wires — however, we would have to have a very sensitive electrical instrument to register this interaction. According to the laws of unlike poles at every point along the separated wires, the unlike poles will attempt to reach and unite with one another and consequently an electrical stress will be set up across the insulation of the two adjacent wires. (It will depend upon the value of the voltage and the strength of the insulation whether or not the union of the polarities will be accomplished.) The insulation is called the "Dielectric" because it opposes the passage of electric current. The area of the surface of the wire will be termed the capacity of the condenser because it will determine the numerical value of the electrons and protons opposite to each other and isolated from each other by the dielectric. Now if we should strip the wires of their insulation and with a hammer flatten the wires until they look like long flat ribbons and again bring them in close proximity and then separate them with a thin piece of paper so that contact or electrical connection cannot take place, we again have a condenser, but one of much greater capacity, because (due to the flattening of the wire) we have enlarged areas that are opposite each other — consequently a greater number of electrons and protons are introduced to each other and at the same time current flow is obstructed by means of the dielectric of the paper. The paper is much thinner than the original insulation and the tempting union of the two opposite poles is increased. Thus we have increased the capacity of our condenser. Condensers Source of Trouble We can assume that the capacity of a condenser depends upon the area of the plates opposite each other, the distance between such plates, and the nature of the dielectric separating the plates. We must consider that our condensers are not all low-voltage condensers. Some of them operate at many thousands of volts. Dielectrics of sufficient strength must be used to prevent any actual flow of current through the condenser. Consequently there are many, many features about condensers that must be understood in order that they may be used with safety. Experienced radio men for the most part agree that 90 per cent of all radio and audio amplifier troubles are located in the filter, by-pass, and coupling condensers. Let us consider one of the most misunderstood {Continued on Page 51)