US 1838146 A
Description (OCR text may contain errors)
Patented Dec. 29, 1931 UNITE'DISTF'IATES PAUL a. norsrne, or cnicaeo, I LINoIs, ASSIGNOR 'ro CENTRAL scmmrrrc cou- PANY, A, coaroaArIoN or ILLINOIS PATENT or-Flea ELECTROMAGNETIC DEVICE Application filed December 12, 1929 Serial No. 413,658.
The student of physics and electricity often finds it difficult to grasp the'fundamental concepts of electromagnetism, and it is one of the primary. objects of this invention to provide apparatus of exceedingly simple design which may be'used' to demonstrate in an elementary and convincing manner the printion with the accompanying drawings, in
which I 12 Fig. 1 is a plan View the apparatus; and
Fig. 2is a longitudinal, sectional view of the same taken on the line22 of Fig. 1.
About a century ago, the scientist Barlow produced rotation in a star wheeliby causing "11 an electric current to traverse radially over the wheel while placed between the poles of a horse shoe magnet. I
, A few years later, Faraday discovered that he could produce an electric current by rotating ancopper disk between the poles of a steel magnet or electromagnet, the current flowing from shaft to rim, or vice .versaac cording to the sense of-rotation. Sliding con tacts were used on the shaft and the periphery of the diskfto conduct away the current gener c. i 1 i I A rotating copper disk placed/m a magnetic field at right angles to the .planeof the disk has for many years been used to demonstrate the operation of Lenzs law and the resultant efiectof a magnetic brake.
This invention combines into one apparatus a structure especially adapted to the requisites of pedagogics which can be used to demonstrate the classical experiments referred to above of Barlow and Faraday and the operation of Lenzs law. I
This specific illustration and correspondingly specific description are used for the purpose of disclosure only and are not to be taken as imposing a limitation upon the scope of the invention except as required by the prior art.
The apparatus in one of its forms com- 1 prises a base preferably of wood, progive to the base a convenient clearance from its means of support. A permanent magnet 12, preferably of chrome steel, is removably secured to the base by clamps 13 and 14 which are U-shaped in form and have their upper arms of sufficient length to engage the upper face of the magnet as at 15.. The clamps are fastened to the base by counter sunk bolts. 16 provided with securing nuts 2 17 and thumb nuts 18. p. Y
I The ends of the magnet 12 are brought close together at 19 and a copper disk20 is mounted in a jawlever 21 for'rotation between the poles of the magnet, Frictionless conical bearings 22'are provided on the jaw arms for engaging the shaft 23 of the disk, and have lock nuts 24 to maintain roper adjustment. I v
A U-shaped ulcrum piece 25 secured to the base by a screw 26carriesthe lever 21 by means of the stud screws 27 and permits the diskto be raised out of the magnetic field by simply applying pressure on the end of the lever. A pin stop 28 serves to fix the normal position of the'disk. t
The base 10 is provided with a mercury trough 29 into which the rotating disk 20 dips and electrical connection is made between the mercury in the trough and the binding post 30 by a screw 31 and conductor 32. The shaft of the rotating disk 20 is in electricalconnec- .tion with a second binding post 33 through the lever 21, fulcrum 25, screw 26 and a-conductor 34. In this way, an electrical current can be made to pass radially through the disk from the shaft to the periphery, and vice versa. 7
When the apparatusis used as an elementary electric motor, the bindingpostsBO and 33*are connected to a suitable source-of current, such as a six volt storage cell, through a rheostat capable of carrying a fairly large current; A carbon compression rheostat is well suited for this purpose. When the current isturned onjthddisk will rotate in a direction depending upon that of the magnetic field and of the current. j A reversal of direction of either thema-gnetic field or the driving current will result in a rotationref the .diskin an opposite direction, while a reversal of both will leave the rotation unchanged.
'vided with knobs 11 at its four corners, which i I A radial stripe 35 on the disk aids in clearly showing the rotation of the disk.
Faradays dynamo experiment with a rotating copper disk may be readily shown by connecting the binding posts 30 and 31 to a gal vanometer and then spining the disk by hand. A current is thereby induced which may be detected by the galvanometer. At constant rotational speed, a steady deflection will be registered on the galvanoineter, its magnitude depending upon the strength of the magnetic field and the speed of rotation.
The magnetic brake effect may be clearly shown by this apparatus by setting the disk into rapid rotation when tilted out of its normal position and then lowering it into the magnetic field. In this experiment, the mercury contact has no importance and the braking action is caused solely by the fact that a conductor is being moved across a magnetic field. By the operation of Lenzs law, currents are induced which tend to oppose the movement of the conductor, which in the case of a rotating disk are called eddy currents.
Inasmuch as the magnet 12 may be readily removed from the base, it is an easy matter to reverse the magnetic field by inverting the magnet, which will cause a rotation of the disk in the opposite direction in the motor experiment and in the dynamo experiment will cause the galvanometer to be deflected on the other side of the Zero mark. The mercury contact which engages the periphery of the rotating disk provides a frictionless electrical contact which enables a more striking demonstration of the motor and dynamo experiments to be made.
The fact that the disk may be readily moved in and out of the magnetic field provides a convenient structure for making the experiments and is exceptionally useful in the magnetic brake experiment.
I claim as my invention:
1. An electro-magnetic device comprising in combination a base, a mercury trough in the base, a rotatable metallic disk dipping in the mercury, bearings for the disk, means for bodily lifting the disk and bearings from the trough, and a permanent magnet having its poles 011 opposite sides of the disk.
2. An electro-magnetic device comprising in combination a metallic disk, a magnet having its poles on opposite sides of the disk, and means for temporarily removing the disk from the magnetic field, including a lever rotatably carrying the disk.
3. In a device of the class described, the combination of a rotatable disk having an axial hub, means for setting up a magnetic field through the disk, and a fulcrumed support equipped with frictionless bearings engaging the hub adapted to raise and lower the disk from the magnetic field.
4. An e1ectro-magnetie device comprising in combination a rotatable metallic disk, a
bifurcated lever carrying the disk, a fulcrum for the lever whereby the disk may be raised and lowered, a sliding contact for the periphery of the disk, adapted to be connected to an external circuit, and means for creating a magnetic field intermediate the sliding con tact and the center of the disk.
5. An electro-magnetic device comprising a base, a mercury contact in the base, a rotatable metallic disk dipping in the mercury, means for connecting the mercury contact and the disk hub to a source of electrical energy to conduct a current radially through the disk, means for creating a magnetic field intermediate the mercury contact and the disk hub, and a bifurcated lever carrying the disk adapted to be rocked upon its support to raise the disk out of the magnetic field.
6. In an electro-magnetic device, the combination of a base, a horseshoe magnet removably secured to the base, a metallic disk mounted for rotation between the poles of the magnet and means supported 011 the base for removing the disk from and reinserting the same in the field of the magnet.
7. In a device for demonstrating certain fundamental principles of electro-magnetism, the combination of a base, a lever support mounted on the base adapted to pivotally support a lever, a lever carried by the support equipped with arms having frictionless bearings, a metallic disk mounted be tween the arms of the lever and rotatably supported thereby, means for creating a magnetic field through the disk when the latter is in its normal operative position, said disk being adapted to be raised from the magnetic field when the lever is rocked on its fulcrum.
8. In a device for demonstrating Barlows wheel, Faradays disk and the operation of Lenzs law, the combination of a base, amercury trough in the base, a rotatable metallic disk dipping in the mercury, means for creating a magnetic field intermediate the mercury trough and the disk hub, and hearing supports for the disk adapted to be bodily lifted with the disk from the magnetic fiellcil Without disturbing the rotation of the In testimony whereof, I aflix my slgnature.
PAUL E. KLOPSTEG.