{"id":2452,"date":"2019-11-21T15:04:36","date_gmt":"2019-11-21T14:04:36","guid":{"rendered":"https:\/\/www.historicalcollections.deib.polimi.it\/?page_id=2452"},"modified":"2020-11-20T06:59:33","modified_gmt":"2020-11-20T05:59:33","slug":"ruhmkorff-app","status":"publish","type":"page","link":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/collezioni\/elettronica-collezioni\/ruhmkorff\/ruhmkorff-app\/","title":{"rendered":"RUHMKORFF COIL"},"content":{"rendered":"
\n
\n
\n
<\/div>\n
\n

The induction coil, known as \u201cRuhmkorff Coil, belongs to the transformers family and it had a leading role in the history of electromagnetism as a current generator. More precisely, it is a type distributive discharge spool. This type of transformer is used to produce high voltage pulses starting from a low voltage direct current source. To produce the flow variations needed to induce voltage in the secondary coil, the flow of direct current in the primary coil is repeatedly interrupted by a vibrating mechanical contact called interrupter.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

\n\t<\/path>\n\t<\/path>\n\t<\/path>\n<\/svg><\/div>\n<\/div>
\n
\n
\n
\n

Insights<\/h2>\n

The inductive coil (or transformer) consists in two solenoids of insulated copper wire\nwrapped around a single iron core. One of the solenoids, called \u201cprimary winding generator\u201d is made up by tens or hundreds of turns of enameled wire, the other solenoid, called \u201csecondary winding generator\u201d, consists in several thousand coils of thin wire.
An electric current that runs along the primary creates a magnetic field, while the\nsecondary is coupled magnetically thanks to the iron core. The primary winding behaves\nas an inductor, storing energy in the associated magnetic field. When the electric current is suddenly interrupted, the magnetic field drops rapidly and, because of the electrical induction, this cause a high level impulse across the secondary.
Thanks to the high number of coils of the secondary winding, the impulse generated\nhave a voltage of many thousands of volts: this voltage is enough to generate a spark or\nelectric discharge around the air between the terminals of the secondary.
To enable the transformer to operate, the direct current must be intermittent to create the variation of the magnetic field needed for the induction. To achieve this, the Ruhmkorff Coil uses a vibrating metal foil called \u201cinterrupter\u201d to rapidly open and close the primary winding.\nThe voltage in the secondary is induced both when the circuit opens and when it closes.\nThe current variation is faster when the circuit opens so the impulse in the secondary at the opening is much greater. A capacitor is located parallel to the switch to damp the\nelectric arc between the contacts and allow a faster opening and therefore a greater\nvoltage.
The secondary winding is devised so as not to show great differences of potential\nbetween the turns, to prevent the coils isolation from being damaged by the high\nvoltages thus generated .
The primary is wrapped around the core and then insulated from the secondary with a\nthick layer of paper or rubber. Each section of the secondary is insulated with an envelope of paraffin, connected to the next section and then inserted on the primary. The voltage developed in each section isn't enough to draw an arc between the different sections.
To avoid any eddy current, the iron core is built with a bundle of iron wires covered in lacquer to insulate them electrically. Such a construction avoids the creation of eddy current perpendicular to the magnetic axis.
Inductive spools were used to generate the high voltage needed for the operation of the first discharge tubes and the cathode ray tubes used for the research on the X-ray. 
Hertz used the inductive spool to emonstrate the existence of the electromagnetic waves theorized by James Maxwell. Inductive spools were also used by both Tesla and Marconi in their radio wave research work. Their major practical uses were as radio transmitter for the wireless telegraphy, and to provide energy for the cold cathode of Xray tubes. Since 1920 they were replaced by vacuum tubes.
Currently, the inductive spool is still used in the ignition system for internal combustion\nengines. A reduced size version of the inductive spool pilots the xenon flash used in cameras and strobe lamps.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"","protected":false},"author":14,"featured_media":0,"parent":2449,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"pro\/page-templates\/full-width-page.php","meta":{"footnotes":""},"class_list":["post-2452","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/pages\/2452","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/users\/14"}],"replies":[{"embeddable":true,"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/comments?post=2452"}],"version-history":[{"count":5,"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/pages\/2452\/revisions"}],"predecessor-version":[{"id":3585,"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/pages\/2452\/revisions\/3585"}],"up":[{"embeddable":true,"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/pages\/2449"}],"wp:attachment":[{"href":"https:\/\/www.historicalcollections.deib.polimi.it\/en\/wp-json\/wp\/v2\/media?parent=2452"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}