» Rheostat (0399)
Immagini
DESCRIPTION
Exhibit 399 is a rheostat, a variable electric resistance; its value depends on the position of the slider that moves along the winding. The maximum value is 4.5 Ω. See exhibit 111.
This type of rheostat can be used as a shunt to measure the resistance of a galvanometer using the method of half deflection as illustrated in design-2. Upon closing the switch
(), and leaving open
(),
the current
() that flows in the galvanometer is
Where,
R = known resistance inserted in the circuit
G = unknown resistance of the galvanometer
E = d.d.p.
If (θ) is the rotation angle of the index of the galvanometer
one has:
where k is a constant of the galvanometer
Now closing switch
, one chooses a resistance from the adjustable rheostat (shunt)
(S) such that the deflection becomes half
(),
then() is given by:
From (i) e (ii):
For R much greater than S one has
Thus
ISCRIZIONI
- Su una etichetta: Ing. S.Belotti & C. S.A. Milano tipo 195 n.o 20991 Ohm 4,5 A. 2,25 Carico -------
Dati Catalografici
Data di costruzione: | --- |
---|---|
Data di carico: | 1937-8-5 |
Nr. Inventario: | 4858 (Generale dal 1874) |
Costruttore: | Belotti |
Materiale: | metallo, mica |
Dimensioni: | Lunghezza complessiva: 27 cm; Larghezza: 10 cm |
Conservazione: | cattivo (manca l'avvolgimento) |