From a practical point of view, the magnetic property of an electric current is of great value to man. It is this property that is utilized in the dynamo for the generation of large currents of electricity. It is also this property that enables man to utilize the driving power of the electric motor in the manufacturing industries

Begeman, L.

University of Northern Iowa

Science Bulletin Volume 3 Number 9 Article 12 5-1931 The Magnetic Effect of an Electric Current L. Begeman Iowa State Teachers College Follow this and additional works at: https://scholarworks.uni.edu/science_bulletin  Part of the Health and Physical Education Commons, and the Science and Mathematics Education Commons Let us know how access to this document benefits you Copyright ©1931 by Iowa State Teachers College Recommended Citation Begeman, L. (1931) "The Magnetic Effect of an Electric Current," Science Bulletin: Vol. 3: No. 9, Article 12. Available at: https://scholarworks.uni.edu/science_bulletin/vol3/iss9/12 This Contents is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Science Bulletin by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. Offensive Materials Statement: Materials located in UNI ScholarWorks come from a broad range of sources and time periods. Some of these materials may contain offensive stereotypes, ideas, visuals, or language. IOWA STATE TEACHERS COLLEGE 7 tudes, middle latitudes could be intro-duced. Of course, these terms will not in the ms cl ves give the ch i ldren the conect ideas of climatic conditions in the various zones but at least they do not hamper by implication. This invcstiga.tion might with profit be carried much further if those inter-ested would gi.ve the test to their stu-dents and send in the results. Alison E. Aitchison. THE MAGNETIC EFFECT OF AN ELECTRIC CURRENT From a practical point of view, the magnetic property of an electric cm-rent is of great value to man. It is this propmty that is utilized in the dynamo for the generation of large cur-rents of electricity. It is also this property that enables man to utilize t h e driving power of the electric motor in tho manufacturing industries. It may be interesting to know that the magnetic property of an electric current was not discovered until twen-ty years after Volta invented the elec-tric pile, b y mean s of which the first real current of · electricity was experi-mentally produced. It was in the year 1819 that Christian Oersted, a professor in the University of Copenhagen, first demonstrated that an electric cmrent running through a conductor held over and parallel to a magnetic needle would cause the needle to rotate from a north and south position into an east a.nd west position. A description of this ex-periment is found illustrated in most high school texts on physics. The ex-periment is r eadily duplicated in a simple way by bringing a magnetic compass (fig. 1) inside a coil of copper wire through ·which the current from a single dry cell is passing. When the current is passing from north to south over the compass needle, the north-seeking end of the needle will deflect to the east. As soon as the current is reversed the north -seeking end will de-fleet to the west . The right-hand rule for determining the direction of deflec-tion of the needle in this experiment was first stated by Ampere. ~ 1'I Fig. 1 In · important electrica.l work it is often necessary to know the direction of a current in a wire ,1-hcn the gen-erator, battery, or dynamo, is not at hand. Oersted's experiment gives one a sure method of solving the problem. All one needs to do is to t urn a part of the conductor carrying the current into a north and south direction and bring a magnetic compass under it. If the north-seeking encl of the compass needle turns to the cast, the current is flow-ing from north to south. If the north-seeking end turns west t he current is flowing in the contrary direction. Oersted showed that the magnetic ef-fect of an el ectric current upon a magnetic needle is unhindered when glass, wood, stone and various other materials are brought between them. Oersted's experiment created much en-t husiasm throughout the scientific world. It was repeated everywhere in scientific circles and created much zeal for fmthcr research on the subject. A year after Oersted's discovery, Arago, a noted Parisian astronomer and ph ysicist, found experimentally that a conductor carrying an electric current would attract iron filings. (Figure 2). 8 SCIENCE BULLETIN He " ·as t he first to state definitely t hat an electric current is a magnet. In 1822 Sir H umphrey Davy, t he noted Engli sh scientist, found that the filin gs attracted by a conductor carrying an electric cunent arranged themselves in cirnles. This ,Yas the fir st hint of t he fact tha.t the magnetic field of an elec-tric current (figure 3) consists of cir-1!B~1b GJ Fig. 3 cular lines of force. The simple ap-para tus illustrated here consists of a p :ece of car dboard firmly fixed in a horizonta l position. A fixed copper wire passes perpendicularly through its cen-t er. ·when a. current from two dry cells i s sent through the wire, very fine iron filings sift ed over· the cardboard will arr a.nge t hemselves in concentric circles a.round the wir e when the cardboard is gent ly tapped. Ampere " ·as struck by the fa.ct that th e magnetic force of a.n electric cur-r ent acted in a pla.ne a.t right angl es to the dii-ect ion of the current. This led him to t ry to intensify the mag-11etic effect of a. current upon a mag-11 etic needle by wi11ding the conducting wire into a coil. He found tha t the effect wa.s grea tly increased. By this expe1·iment he laid the foun dation fo r t ho electromagnet. Am pere added another contribution to the knowledge of electro magnetism whe 11 he stated the la.ws of parallel currents. In figure 4 two parallel wires a.re strnng side by side and are sup-posed to b e free to move laterally eith-er toward or a w.ay from each other. Amper e discovered that when the cur-' J 1 J Fig. 4 rents are flowing in t he same directions in two such wires they a ttract and approach each other. Also, when the currents arn flowing in opposite direc-t ions, the wires rnpel each other and move apart. H e rightly observed that this mechanical attraction and repul-sion of two such wires carrying cur-r en t s is due to the in ter action of the magnetic fields which sunound th.e wires. A b eautiful experiment illus-tra ting the mechanical at traction of currents of electricity ca.n be perform-ed by means of a loosely wound coil of wire suspended perpendicularly from a support. The lower end of t he coil should dip into a cup of mercury. When a current is sent through such a coil, it at once contr ac t s in length due to the attracting force between its suc-cessive turns. The renowned F a.raday, known as the fo r emost experimentalist of the nine-teenth century, also contributed large-ly to the fundamental concepts of elec-· tromagnetism. H e devised the experi-N t Figure 5 IOWA STATE TEACHERS COLLEGE 11 ment (fig. 5) which demonstrates that a magnet pivoted parallel to an elec-tric conductor will rotate when a cur-rent is sent through the wire. When the magnet has its north-seeking pole at the top and the current is sent down the wire, the rotation will b e clockwise to one looking downward. FTOm this experiment we get the first suggestion of the modern electric motor. It will be impossible in this brief article to go into the more important work of Faraday pertaining to current induc-tion, which led to the modern dynamo. Both Ampere and Arago found by experiment that an elongated coil (fig. ·6) when can ying a current possesses Figure 6 all the properties of a bar magnet. A -coil of this kind is called a solenoid. Wihen delicately suspended it will turn and take a north and south direction_ with r eference to the earth's surface. It is evident that the solenoid is the simplest form of an electromagnet. It was not until 1825 that William Sturgeon, a shoemaker of Lancashire, England, described the first real electro-magnet, consisting of a solenoid with a soft iron core. Sturgeon's magnet could lift nine pounds, which was ,about twenty times its own w eight. Stur-geon's description of his electromagnet created .a tremendous amount of inter-•est in scientific circles. A student in general science or high school physics should be given the op-portunity of constructing for himself a small electromagnet. Nothing will con-tribute more to his interest in the sub-ject. Such a magnet can b e made in a few minutes by simply wrapping about twenty turns of cotton-covered wire around a wrought iron bar about three inches long and one-fourth inch in diameter. The pole of .a small elec t ro-magnet of this kind will pick up many mo,e iron tacks than the pole of a large steel bar magnet. The complete development of the electromagnet for practical uses must be credited to Joseph Hemy, an Amer-ican physicist. Hemy was the first to use silk-wound insulated ,1·ire around his iron cores. In 1829 he constructed magnets with many layer s of wire in their windings. 'l'hese magnets were extremely powerful, lifting as much as fifty times their own weight. It was H em y also who first used the electro-magnet for transmitting signals to a distance, thus lay ing the foundation for the telegraph, invented by Morse in 1837. A more complete stud y of the history of electromagnetism and of the biog-raphies of the scientists mentioned above would make an excellent project for a high school class in physics. L. Begeman. STIMULANTS The state law requires the teaching of the effects of narcotics and stimu-lants. Most teachers would be glad to comply with the law if they were cer-t ain that they could present reliable information. The difficulty in the past has been that most of thP. information available was merely propaganda and not based on scientific fact. The tobac-co companies have always been able to secure statements from people of prom-inence who were tobacco users to the effect that tobacco not only did t hem no harm but actually proved of value. Their statements were not based on scientific evidence, and many of them were undoubtedly purchased. On the other hand much of the ''anti '' litera-ture has been just as ridiculous, unsci-entific, and untruthful. Boys have been 

The Magnetic Effect of an Electric Current

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The Magnetic Effect of an Electric Current

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