Question

In the primary circuit of potentiometer the rheostat can be varied from $0$ to $10\Omega$. Initially it is at minimum resistance (zero). Find the length $AP$ (in m) of the wire such that the galvanometer shows zero deflection.

Answer 1

when deflection is zero $\Rightarrow$ voltage of secondary cell=voltage drop on the balancing length of the wire AB
voltage drop on the balancing length of the wire $\Rightarrow$i$\rho$X
where i= currnt flowing in primary circuit
$\rho$=resistance per unit length of the wire
X=balancing length of wire AB
when deflection in galvanometer is zero$\Rightarrow \frac{9}{2}=\left(\frac{10}{10}\right)\left(\frac{9}{12}\right)x$
$x=6m.$