Question

The potentiometer wire AB shown in figure (32-E26) is 40 cm long. Where should the free end of the galvanometer be connected on AB so that the galvanometer may show zero deflection ?

figure (32-E26)

Answer 1

If the wire is connected to the potentiometer wire so that

$\frac{R_{AD}}{R_{DB}}=\frac{8}{12}$

then according to Whitstone's bridge, no current will flow through galvano meter

$\frac{R_{AD}}{R_{DB}}=\frac{L_{AD}}{L_{DB}}=\frac{8}{12}=\frac{2}{3}$

(Acc. to principle of potentio meter)

$L_{AD}+L_{DB}=40cm$

$\Rightarrow L_B\frac{2}{3}+L_{DB}=40cm$

$\Rightarrow \frac{5}{3}{L}_{DB}=40cm$

$\Rightarrow L_{DB}=40\times \frac{5}{3}=24cmfromB.$