Radio mirror (Jan-Oct 1923)

May 5, /p£? RADIO DIG E S T First Steps for Beginners in Radio Chapter I — Laws of Electricity Used in Radiophony By Thomas W. Benson, A. M. I. R. E. A THOROUGH understanding of Radio phenomena demands a knowledge of the laws of electricity. Radio being but a special application of this useful servant of man depends thereon for its fundamental units anil laws. Athough having symbols and terms distinctly its own, Radio phenomena will be more clearly understood in the light of the paragraphs to follow. Electromotive Force In order that electricity might Bow in a wire of circuit it is necessary that a difference of potential or electrical pressure exist between two points connected by a conductor. To measure this potential TUBE FILAMENT 6QHMS BATTEftr t^ VOLTS RHEOSTAT 40HM& or electromotive force (E.M.F.) we make use of the volt which is then the unit of pressure so to speak. Thus we find that a dry cell has a voltage of 1%, that is, the pressure at the terminals of a battery tending to make a current flow in any circuit connected to it, is 1% volts. There is no fixed unit of voltage but is arrived at by other means. Now when we connect an electrical device to the dry cell, let us say the filament of a YVD1-11 tube with a rheostat in series as shown in Figure 1, a current will flow. The amount of current flowing is measured in amperes which is the quantity of current. It should be made very clear that the voltage is forcing the current around through the rheostat and filament but the amperes is the amount of current flowing. Resistance Whenever a circuit is completed the material or conductor through which the current flows offers a certain resistance or tends to hold back the current. This effect is measured in ohms, the unit of resistance. Going back to our illustration we find we have a very fine wire in the tube and also a rheostat made of wire that has OR.Y CELLS IN SERIES DRY CELLS 1 MULTIPLE N + + + C^ fp + ~o ^_ — -o -k -o STORAGE CELLS IN SERIES STORAGE CELLS IN MULTIPLE a high resistance. By regulating the holding back effect of the circuit we can control the amount of current or amperes flowing. Thus by turning the rheostat handle so there is less resistance for the voltage to overcome the current through the filament increases and it gets hot. Ohm's taw The law of current flow is known as Ohm's Law, the most fundamental law of electricity, and also, the most simple. Put into words, the current in a circuit varies directly as the voltage and inversely as the resistance. Put in the form of a formula we have: B R That is, the current in amperes (I) is equal to the voltage (E) divided by the resistance (R) in Ohms. Let us see how this works out. When resistances are connected in series their total resistance is equal to the sum. In Patents Procured and Trade-Marks Registered. Advice and terms upon request. ROBB, ROBB & HILL. 1417 Hanna Bldg., 956 McLachlan Bldg., Cleveland. O. Washington, D. C. /%WE REPAIR WD-11, $3.50 and OTHER VACUUM TUBES Excepting VT-I and VT-II MAIL ORDERS Solicited and Promptly Attended To [ & H RADIO GO. 516 Clinton Avenue NEWARK, N. J. BEGINNERS will find the accompanying series by Mr. Benson very helpful in learning the rudiments of the popular science of Radiophony. His articles yet to appear are: Chapter II — Radio Waves and their Propagation. Chapter III — Pointers about Aerials and Grounds. Chapter IV — About Condensers and Inductances. Chapter V — Tuners and How to Tune Your Set. Chapter VI — About Crystal Detectors. Chapter VII — Tube Detector Theory and Operation. Chapter VIII — The Regenerative Detector. Chapter IX — Radio Frequency Amplification. . Chapter X — Audio Frequency Amplification. Chapter XI — How Super Regeneration Is Accomplished. Chapter XII — Reflex Circuit Operation. Chapter XIII — About Headsets and Loud Speakers. Chapter XIV — Batteries Used in Radiophony. the circuit we have say a 4-ohm rheostat and the filament of the tube with a resistance of 6 ohms. This gives a total of 10 ohms when all the rheostat is in. To determine the current we simply divide the voltage 1.5 by the resistance, 10 ohms giving .15 amperes. Say we cut the rheostat out entirely leaving the battery connected direct to the tube, this gives but 6 ohms and on figuring it out the current will be one-quarter ampere. Since the current is equal to the voltage divided by the resistance it also holds that when voltage and current are given the resistance is equal to the voltage divided bv the current or: E For instance, the UV 200 takes 1 ampere filament current at 5 volts. To determine its resistance divide voltage, 5, by current 1, and we find its resistance is 5 ohms. Going one step further it will be clear that the product of the current and resistance should equal voltage. We can express this as E=IXR. Resistance In Series It has been stated that when resistances are in series that is when the current must flow through one after the other the total resistance is equal to their sum. However, when they are connected in parallel or so W. T. 501 Peanut Tubes, 4 V. </x Amp. with Adapter $2.75 (Use storage battery or 3 dry cells in series) R. V. T. 5-6 V. Detectors 2.75 R. V. T. 5-6 V. Amplifiers 3.35 (Sent on receipt of price. No C. 0. D. orders accepted) I Tube Regenerative Receiving Set with Detector Tube and 3000 Ohm Headset. VERY SPECIAL VALUE 29.75 LUX MANUFACTURING CO. 1045 North Wells Street. CHICAGO, ILLINOIS HERE IT IS Just What You Have Been Looking For A VARIABLE RADIO RESISTANCE THAT MOUNTS ON PANEL IN A JIFFY ir^^ Patents Pending. Real Radio Fans, In the building of their sets, will more than appreciate this device, which gives them a variable resistance which is adaptable for use in all Radio Hook-ups — in the grid circuit — as amplifier coupling resistance for both radio and audio frequency — "B" battery resistances — antenna shunts — timed loop circuits — resistance couplers for both radio and audio frequency, and many other places in the radio hook-up that the amateurs' ingenuity will suggest. Has switch lever and seven carefully calibrated values of resistance of % megohm each between terminals. Protecting bak elite discs assure permanency of moisture-proof India ink resistance. Don't guess — it is important to have resistances properly adjusted to function with your other apparatus to get the best results from all tube sets. A Premier Variable makes this sure and easy. Code No. 250. Pries $1.50 each DISTRIBUTORS— We make a most complete line of radio parts. Some territory open for live, responsible concerns. PREMIER ELECTRIC COMPANY Manufacturers Est. 1905 3800 Ravenswood Ave. Chicago, 111. that the current can branch and flow through them simultaneously a different rule holds good. When the resistances are all alike the resulting resistance of the set is equal to the resistance of one divided by the number in parallel. Thus, putting two like resistances in parallel cuts the resistance in half, three in parallel gives but one-third the resistance of one unit. On the other hand if resistances of unlike value are connected in parallel it complicates matters somewhat and we must fall back on formulae again. When two unlike resistances are in parallel the following holds good: RXR R (total resistance)= R+R That is, their product divided by their sum. When more than two unlikes are in parallel the formula becomes: 1 R (total resistance) = 1 1 1 Ri Rs R3 Which can be readily solved. The reader may doubt the value of these formulae to the experimenter but their value will be apparent when one wishes to build up say a given grid leak from a number of smaller or larger leaks. Standard of Resistance The standard of resistance being an ohm, it is advisable when high resistances are used to use other units. Thus the megohm is used for one million ohms. A halfmegohm leak then has a resistance of half of one million or 500,000 ohms. The resistance of a conductor varies as its length, diameter and material. Increasing the length of a wire will increase its resistance and vice versa. Increasing the size of wire reduces its resistance and increases the current carrying capacity. The use of special materials, such as German silver, nichrome and constantan, gives wires having high resistances. Units of Energy and Power Having obtained an idea of the relationship between the units of pressure, current and resistance, we can go on to a consideration of the units of energy and power. We have seen that a certain voltage is required to force the current through the circuit, and since the current does the work we must consider both voltage and amperage in determining the energy expanded in the circuit to do work. (Continued on Page 14) Hear On Cfi*V«tal We receive progJ ^^»» ^**,y»*«»» rams from Atlanta Minneapolis, Davenport, FortWortht Dallas, Kansas City, St. Louis, Denver on Crystal without batteries. Usual crystal set requires only easy, inexpensive changes. Send stamp for further information or 31 for copyright drawings and instructions. Everything dearly explained. ^Satisfaction GUARANTEED. . Leon Lambert, sof jtouth Volutsia, Wichita, Kan, Federal Standard Head Sets are made nuitk 2200 Ohms and 3200 Ohms resistance. 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