» Battery Comparison Box (0251)

Immagini

DESCRIPTION

Exhibit 251 is an instrument which employs the Poggendorff (or opposition) method to compare electromotive forces. In particular if Fe1 and Fe2 are the electromotive forces of two batteries, one can measure the ratio Fe1/Fe2 so that knowing Fe2, one determines Fe1. In reference to the figure, copied from ref.1, one sends a constant current in the wire AB using battery P. Now VA is greater than VB and (VA-VB) must be greater than both Fe1 and Fe2 by making the resistance AB large enough with respect to the rest of the circuit (BG0RPA). In the figure Fe1 tries to send a current in opposition to that due to P (In the figure the polarity of Fe1 is to be inverted) That condition is satisfied by varying the position of X=l1 until the galvanometer G indicates zero. Then the same is done substituting Fe2 for Fe1 and noting l2.The ratio of Fe1 to Fe2 is the same as the ratio of the lengths l1 to l2. para> In this instrument there are separate connections for Fe1 and Fe2 and a commutator (upper left in photo 2) to switch between the two. The instrument is enclosed in a wood box in which are visible the the two variable resistances realized with manganina wire and all the terminals.

ISCRIZIONI

Su una targhetta è inciso il nome del costruttore: Eisentraeger

BIBLIOGRAPHY

[1] E.Perucca - Fisica Generale e Sperimentale - Volume secondo - IV edizione - 1942 - pag. 623

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