A Simple Demonstration Stroboscope and Circuit for Charging Condensers to High D.C. Potentials G. H. WAGNER a n d W. G. EVERSOLE S t a t e University of Iowa, Iowa City, Iowa
THE stroboscope is an instrument used to observe the successive phases of a periodic motion by means of synchronized flashes of light. The motion must he periodic and of a high enough frequency (about 16 per second) to utilize the persistence of vision. The applications of a stroboscope and its various forms have been described.' The purpose of this article is to describe a stroboscope of simple design which was constructed from inexpensive and easily accessible materials. Figures 1 and 2 show the complete apparatus with circuit. An automobile distributor mounted in such a
neon tube flashes, which depends on the speed of the motor, was measured by means of a revolution counter on the distributor shaft, since each revolution of the shaft corresponded to six flashes in the tube. A reflector from a discarded electric heater supported the neon tube. Any small gas discharge tube is suitable for use as a light source. For frequency determinations or observations of
periodic motion, the frequency of the flashes was varied by means of a variable resistance in series with the motor. Stop watch observations of the dials of the revolution counter gave the necessary data for computing the frequency of the flashes since: way that its shaft could be rotated by means of a '/60 H.P., 110-V.D.C. motor2 served as an interrupter for the six-volt primary current of an automobile spark coil. (The spark coil and distributor were obtained from a salvage shop for about two dollars.) The frequency of the 'EDGERTONAND GERMESHAUSEN. "The stroboscope and high-speed motion picture camera as research instruments." Am. Inst. Chen. Ene.. 30. 420-37 (Mav. 1934): B a s m D KNOWLES. "The stro6&loi," Elec. 3:.28; 250-3 '(April. 1931). = A n y variable speed motor with sufficient powcr could, of course, be used.
no. of flashes/sec. = (no. of rev./sec.) X (no. of Bashes/rev.)
Any frequency of which the actual frequency is a multiple causes the objects to appear stationary. However, multiples of the actual frequency displace the objects closer together. Thus the absolute frequency can be determined. The frequency limits of the stroboscope are determined by the speed of the motor and the size of the pulleys. With two variable resistances of 195 ohms each in series with the motor, a four-inch pulley on the
distributor shaft, and a one and one-half-inch pulley on the motor, the stroboscope used by the authors had frequency limits of 15and 95 flashes per second. An equally important use of the secondary circuit has been for the purpose of charging condensers, which were
used in single-flash photography, to high direct-current voltages (4-8 kiiovolts). This is accomplished by placing a point-plane spark gap in the secondary circuit in series with the condenser to be charged, as indicated in the alternate circuit of the figure.
