$A$ potentiometer wire is $4 \text{ m}$ long and a potential difference of $2 \text{ V}$ is maintained between its ends. The e.m.f. of the cell which balances against a length of $80 \text{ cm}$ of the potentiometer wire is: (in $\text{ V}$)

$AB$ is a potentiometer wire as shown in the figure. If the value of $R$ is increased,in which direction will the balance point $J$ shift?

$A$ potentiometer is an accurate and versatile device to make electrical measurements of $EMF$ because the method involves:

In a potentiometer experiment,when three cells $A, B$ and $C$ are connected in series,the balancing length is found to be $420 \ cm$. If cells $A$ and $B$ are connected in series,the balancing length is $220 \ cm$ and for cells $B$ and $C$ connected in series,the balancing length is $320 \ cm$. The emf of cells $A, B$ and $C$ are respectively in the ratio of:

For the measurement of potential difference,a potentiometer is preferred in comparison to a voltmeter because

In the potentiometer circuit as shown in the figure,the balance length $l = 60 \ cm$ when switch $S$ is open. When switch $S$ is closed and the value of $R$ is $5 \ \Omega$,the balance length $l' = 50 \ cm$. The internal resistance of the cell $C'$ is : .............. $\Omega$