Stroboscope

An image taken using a short-lasting estroboscope light.

The stroboscope (Greek: στρόβος [strobos] 'swirl' + σκοπέω [skopéō], 'I observe') is an instrument invented by the Austrian mathematician and inventor Simon von Stampfer around 1829, which allows to visualize a rotating object as if it were stationary or rotating very slowly. This principle is used for the study of rotating or vibrating objects, such as machine parts and vibrating strings. It was developed at the same time that the Belgian physicist Joseph Plateau was making his phenakistiscope known.

It allows you to turn a light on and off, in a given period, the number of times you want. This device is widely used in nightclubs, on airplanes, and in film production to give the impression of fast movements.

In essence, a stroboscope is equipped with a lamp, normally of the xenon gas discharge type, similar to those used in photography flashes, with the difference that instead of a flash, it emits a series of consecutive flashes and with an adjustable frequency. If we have an object that is rotating at N revolutions per minute and we adjust the frequency of the strobe to N flashes per minute and illuminate the rotating object with it, this, when illuminated always in the same position, it will appear to the eye as immobile.

If the flash frequency does not exactly match the rotation frequency, but is very close to it, we will see the object move slowly, forwards or backwards depending on whether the strobe flash frequency is, respectively, lower or higher than the strobe frequency. rotation.

A well-known application of this instrument is adjusting the speed of vinyl record players. These devices have marks drawn on the edge of the turntable, marks that are illuminated by the light of a gas discharge lamp, in this case neon, powered by alternating current from the 50 Hz or 60 Hz electrical network (in most American countries). As the number of marks is calculated so that, with the correct turning speed, 50 or 60 marks will pass each second in front of the neon lamp, the marks appear immobile when the speed is indeed correct. Most turntables have two bands for an identical rotational speed, to adjust this well outside with 50 or 60 Hz alternating current.

The stroboscope is also used to verify the speed of rotation of machines and motors of various kinds, without the need for any electrical or mechanical coupling.

Conversely, if various images corresponding to different phases of the motion of an object are pasted onto a rotating disk and illuminated with the strobe in such a way that a flash is produced each time an image passes before the eye, leaving the plate without lighting during the space between one image and another, the result will be that the object will be observed in motion. Cartoon movies are based on this principle, called the stroboscopic effect.